Failing my reboot idea, I'd probably retrofit it into a loose follow-up to the existing films:
Roughly fifteen to twenty years down the road, Earth is not in pretty shape. The Autobots have been absent from Earth for some time...long enough for Galvatron and his lackeys, Cyclonus, Scourge, and their drone force, the Sweeps, to set down and begin pillaging and plundering the planet entire, scattering civilians like ants away from the major industrial areas. Attempts at a human resistance have been crushed repeatedly and horrendously, and to all appearances it would seem that Galvatron's plans for the planet are nothing more complex than bleeding it dry of every resource it has (given that that there are no more conveniently-buried ancient Cybertronian artifacts on or orbiting the planet anymore)...which means that the extinction of the human race is a certainty unless somebody gets his red-and-blue-armored Autobot @$$ back to Earth to take care of business. Aided once more by Bumblebee and five other new Autobots backing him up, as well as a juvie fugitive sent up for all manner of electronic crimes before Sweeps caved the facility in and a ragged war veteran who's lost enough in the chaos to be ready to go out in a blaze of glory himself, Optimus Prime leads an explosive road trip, blasting, slashing, smashing, outrunning, outgunning and outmaneuvering wave after wave of Sweeps in a beeline straight for Galvatron's citadel in Seattle...which may turn out to be exactly what Galvatron wants.
CAST OF CHARACTERS
- Different design/alt mode, necessitated by the fact that obviously some time has passed - he might still be a long-nosed cab, though, but different model. Also would have a bit more personality than he has in the existing movies; he's also the first Autobot to enter the story and the one who picks up Verity as she's wandering about, and as such there's kind of this Yoda aspect to him akin to when we first met that little green bugger back in 1980: the sort of 'mildly-cantankerous-whimsy' facade that masks his true nature from this cynical teen who isn't sure what she's gotten herself into climbing into the cab. His CB handle is "Orion" (nod to G1 there) when we first meet his driver hologram.
- FINALLY FRIGGIN' TALKS...turns out to be a smart mouth as well as a crack shot. Really plays into the 'espionage' aspect of the character; might put him back in a '70s 'muscle car' alt-mode (which would probably fit this particular story better). CB handle is "Gold Bug" (another G1 nod).
- The brooding Clint Eastwood type. Unmarked/undercover car. Spends the first 20 minutes following Optimus and screwing with the audience and making them wonder whether he's actually a Decepticon or just plain bad news (reminiscent of the first 15-20 minutes of "Terminator 2") until he transforms and we realize he's actually an Autobot.
- A lovable-grump hardnose, a lot like Red Foreman. Still, he enjoys a good smoke out in the peace and tranquility of the mountains...even as the timed explosive he just stashed in one of the Sweeps' weapons caches blows off in the distance.
- A real gung-ho crazy. Loves chopping up Decepticons with his saw probably more than just shooting them outright ("Give me your face!...Now the rest of your head!...Those shoulders gotta go, too..."). The one Autobot voted most likely to get himself killed before the movie's over - he's THAT gonzo.
- Separate character from Elita-1. Flippant personality, nasty toward Decepticons, but also Optimus' closest confidant (their history is never really gone into detail, though). Often trading barbs back and forth with 'Bee, so there's kind of something going on between those two, too.
* And one other Autobot I haven't figured out yet.
Humans (really only three that we focus on)
* Verity Carlo (or some variation thereof)
A real snot. First time she tries to hack into a computer terminal it ends up crashing her stolen laptop and giving away her position (thus getting rid of that cliche immediately), leading to her rescue/first encounter with a 'Bot. Ends up pairing off with 'Bee and essentially becomes Frog to his Bandit (minus the romantic stuff, obviously).
* Walter Barnett (or some variation thereof)
A battered man, veteran of a military family and its sole survivor; his son and wife were lost to the Sweeps. Is Optimus' contact in Seattle (using typical CB slang, which Galvatron doesn't pay attention to...presumably).
* Adam Rook/Lazarus (or some variation thereof)
Leader of the resistance...not real keen to having to rely on the Autobots to rescue humankind from oblivion. On the other hand, he notices, the Autobots's WEAPONS make such pretty explosions...
- NOT Megatron resurrected - instead of being the swarthy, snarly "I smell you, boyyyeee!" type, he's cold, aloof, calculating. His obsession with Megatron's death at Prime's hands turns out to NOT be quite the usual revenge one expects...personally, I'd lean more toward the idea of Galvatron as Megatron's "offspring" of sorts, out for revenge against Optimus Prime, but his revenge would not be so much to avenge the death of the "father" he actually hated, but to avenge himself for being cheated of the chance to kill Megatron with his own hands.
- O.K., some blasphemy here...my Cyclonus would be female. Partially because I'd like a female TF in a TF movie to actually be bad@$$, and because the trio of main Decepticons here would also be something of an homage to the Phantom Zone villains in "Superman II".
- As Galvatron is to Zod and Cyclonus here to Ursa, Scourge would be to Non: the near-mute bruiser whose fists (and weapons) do his talking. Not because Scourge is mindless, mind you - he's actually roughly the same in intellect as Cyclonus, he just doesn't see the need to do a lot of talking about it when there's Autobots and humans to kill.
* A messload of Sweeps.
- Drones, and as such no worries about underdeveloped personalities. Still nasty buggers, though. The Sweeps are a lot like the Eradicons from TF: PRIME (or Vehicons or whatever not-anywhere-near-as-cool name they've been given this week) - multiple alt-modes: road-worthy AND flight-capable.
A couple other notes:
* Screen time between 60/40 robots, but that doesn't mean they'll be in robot mode all that time...a lot of times with the Autobots we focus on their holographic drivers. The good of this is that it would allow us to finally spend more time focusing on the robot characters without having to put ILM through hell again; the possible downside of this is that the person playing each Autobot's driver is gonna have to double as that Autobot's voice actor also, meaning the voice actors this time also have to carry an on-screen presence - they don't need to be 'names', necessarily, but they do have to be able to act in front of a camera as well as behind a mike. And the 'road trip' nature of the story also would also emphasize the vehicle modes, too, which again you don't need CGI for all the time, either. Granted, the Decepticons would probably have enough contempt for humans that if they were even to allow "passengers" (i.e. hostages) they wouldn't bother using the holograms on them...but then just having them communicate through their radios or whatever as disembodied voices threatening them to shut up would probably be more fitting for them anyway.
* The seeds for at least the next two films would have to be set in this one so that we're not going back to the "Let's go on another MacGuffin Hunt!" well for the umpteenth time. Rather, the set-up for some MECH-like organization of anti-Cybertronian techno-terrorists would be in motion as certain members of the resistance, particularly Rook/Lazarus, get a little fed up with having to fall back on the red and blue truck guy and the yellow and black car guy to pull their fat outta the fire. This would also pay itself off when Rook's new faction tries to hack into Starscream's lifeless brain trying to gather data out of it and end up accidentally creating a virus that infects some of the Autobots and drives them murderously insane - essentially combining the "Starscream's ghost" concept and the "Hate Plague" concept into one element.
* Unicron I can take or leave, really. He wouldn't be alluded to in this story, anyway (except maybe a passing offhand remark) and would have nothing to do with the connection between Galvatron and Megatron. He might be brought in for a sequel, but it would have to be in a way that circumvents any possible FX-budget issues while at the same time is a little more inventive than, say, a giant space-cloud. On the other hand, I'd be game for the Quintessons as a Gigeresque space-cult who come to Earth with the pretense of aiding Rook/Lazarus in purging Cybertronian life from it, but of course have ulterior motives that don't exactly jibe with humankind's.
* As depicted in this story, human society has become either completely technophobic or forced to adopt older, archaic (by comparison) technological products as a result of the Sweep occupation, given that the Sweeps are capable of monitoring vast computer networks and anything hooked to them. The defense network is completely gone, so the military would be kind of crippled beyond the aforementioned pockets of resistance. Any car that's got OnStar, for example, is a prime target for being tracked, as is any cell phone that has stored information inside it (and by extension, phone lines). The Internet is one big invitation to disaster. This is partially the reason why the Autobots use CB radio and slang to communicate, and also why some of them tend to have older alt-modes (hence having 'Bee back in a classic-car vehicle mode). It's also why Prime would probably be sans trailer once again: the Sweeps, on aerial patrol, will go for any sort of cargo-hauling vehicle searching either for possible hidden stash for the resistance or just plain anything that somebody doesn't want them finding. So in this case having a trailer would be a tactical liability.
* The previous films each sort of start on a small scale and end up getting bigger and bigger before the run time ends. This one'd be a little different: it actually starts on a larger scope where the Autobots are picking off Sweeps, and by the end is pared down to a handful of surviving Autobots against the big three Decepticons - it's the ACTION that becomes more intense as the movie progresses; the fights become more furious and less room for humor is given (even the car chases when we can't afford to have the CGI robots there would hearken back to "The Road Warrior"), because as it goes on the enemies the 'Bots fight are that much more capable. Related to that, the tone would be comparatively light until we get to the end...where we lose about half the Autobots and at the very least Galvatron gets away (so that we don't have to worry about the flogging the back-from-the-dead horse again).