All excellent questions, but it's a lot to unpack so lets see....
1. No official name, but Every TR Leader class figure as well as Fortress Maximus and Trypticon have them. Additionally
Legends God Bomber, Greatshot, Big Powered (Dai Atlus), and Grand Maximus have them as well. Also the Convention Exclusive Shreddicus Maximus (Black PM Prime repaint with skateboard ACCESSORIES). Also the Airlock system was introduced with Siege Omega Supreme and Astrotrain, thus why it is not exclusive to Earthrise. There were no other bots outside of TR, and a few TT Legends however that have the TR connector system, other than obviously Siege Omega Supreme.
2. No. Siege Omega Supreme is quite literally and figuratively the only bridge between both types of systems
3. Not that I am aware of
4. IN the original Series "Scramble City" power was promoted in Japan. The Hasbro toys could do it as well although it was not advertised. Onslaught and Motormaster had base modes that could connect to the original Trypticon. same with Silverbolt and Hotspot to Metroplex. Additionally in robot mode Metroplex had 4 ports (one on each arm and leg) to connect limb-bots for more Scramble Power!
5. I'll leave this for someone else to answer, as I'm not sure.
There is no official connectivity here, but it is a thing of Chaotic Magnificence!
I have Greasepit coming in the mail, and Doubledealer scheduled to arrive August 10. If I can just somehow find Scorponok and Slitherfang before then, I plan to take pics with all the Airlock TF's released so far. I recently purchased TT Big Powered online, the last of the TR/Legends Leaders I needed. Getting them all together for base mode pics is going to be quite a chore though, that may be a Labor Day project.
Bucket/Want List: Botcon 2016 Customization Class Ratchet (G2 Deco), or Customization Class Ratchet (Marvel Comics Deco) **would also be willing to pay for an Unpainted Botcon 2016 Ratchet, TT Legends Fortress Head (only) with working Electronics
Wish List of Modern Combiners: Road Caesar, Monstructor & Dinoking (proper size to fiction), Landcross, Guard City, Battle Gaia, & G2 Defensor. Wish List of Titans:Metrotitan,Majin Zarak