I don't think there could be another three Transformers movies, done well, if they are filmed on earth. IMO, it would be a stretch to think people would come rushing to the box office to see villains they've little emotional attachment to such as Nemisis Prime, Jhiaxus, etc. After seeing DOTM for the fourth time last night, I can't help but feel that is how the movie continuity should end.
If they want to make a 4th installment, I think they could succeed with Unicron. Here's my idea...
TF-4 would be a film shot mostly in CGI, similar to Avatar in that case.
The setting would be 2055 - futuristic enough to allow Sam to still be alive and alert, but to old to be running around fighting alongside the Autobots.
After decades of sparce battles, the Decepticon attacks on earth have, by this point, become extremely futile. With the help of the Autobots, human technology has gotten to the point they now have ships similar to the ones manned by the 'Cons in DOTM. The humans can, more or less, can handle these petty attacks by the 'Cons. Still, human an occassion human life is lost in battle and the pressure from the general public are calling for the Autobots to leave earth, thinking the Decepticon attacks will stop altogether if the Autobots are elsewhere. Even if they do attack, the humans feel they can handle it now. Optimus Prime agrees to take his crew of Autobots elsewhere once they have secrectly constructed a state-of-the-art Autobot ship. (Remember, Transformers are good at building huge objects in an insanely short amount of time.)
During the time of the ship's construction, Optimus uses an object similar to the space bridge pillars. It is a (really) long range radio and he is hoping he will be able to contact intelligent life somewhere else on the galaxy, hopefully on a planet that has energon.
He receives a response from an Autobot crew on an unknown planet in an unknown galaxy. This crew is lead by Ultra Magnus and features Kup, Warpath, and Sandstorm... as well as many (nameless) others.
Elated to receive news from old friends, Optimus flys his Autobots to take refuge on this new planet. Ultra Magnus reveals they too have faught a war against Decepticons, on this planet, and won. He tells the Autobots the planet's name is Unicron, since he heard so many Decepticons utter the phrase "for Unicron," in battle.
Unicron "akwakens" when the Matrix of Leadership, carried by Optimus, arrives. He contacts Octance, Blitzwing, and Astrotrain and provides them with a boost of energon to convince them to fight in order to destroy the Matrix. He revives and reformats many dead Decepticons (Thundercracker, Skywarp, Dirge, Thrust, and Ramjet) into Cyclonus, Scourge, and Sweeps.
The Decepticons unleash a brutal attack on the Autobots, catching them slightly off guard. Optimus gets hit so hard the Matrix falls from his chest and he notices it is glowing instensly. Once the Autobots have driven the 'Cons off the Matrix takes Optimus for a trip (he enters the Matrix). In the Matrix, Sentinel Prime and The Fallen (remember, they were Prime's so they're knowledge is in there) reveal who Unicron truly is as well as his history of devouring planets and his battles with the, now deceased, Primus. The Matrix is in the one energy source powerful enough to overload Unicron's core and destroy him. Only one Autobot, Alpha Trion, has ever attempted such a task and was destroyed in the process. He did, however, destroy Unicron's transformation cog in the process, leaving him stuck in planet mode. Alpha Trion hoped he could destroy Unicron's core with his weapons and felt the risk to possibly save the universe was worth it.
Optimus and Magnus decide to venture to Alpha Trion's ancient, old base, in order to find his route to the core. Kup is left in command of the Autobots.
Trion's base is found in a legendary city named Metroplex which has been abandoned for centuries. Octane, who had been tracking the two Autobots, ambushes them and ultimately kills Magnus. Prime kills Octane and is more determined than ever now that, yet again, one of his closest friends has been murdered.
Upon returning to the Autobot's HQ, Prime tells the Autobots his plan to fly a shuttle to the core and overload it. He wants the Autobots to evacuate as he is unsure of what will happen if he succeeds.
Unicron has commissioned the construction of a new transformation cog which is installed shortly before Optimus begins his trek to the core. The Autobots on the verge of evacuation are mercilessly attacked by the Decepticons who have been promised unlimited energon in exchange for the destruction of the Autobots/Matrix. Optimus is able to take fight in a small shuttle and begins his quest.
Will continue with my next post... it keeps taking my cursor back to the top of my post now.