I think it would be epic if the movie started like this: The NEST team gets signal from Siberia. It is two desepticons that is searching for something (something that we will see later in the movie). So some new autobots that can fly or just the usual autobots gets to Siberia in some way and starting the hunt for the desepticons.The desepticons can be: Mil Mi-24 and Mig 29.When the bad guys realize that some one have seen them, they transform to the vehicle mode and try to escape.Becouse Mig 29 is a jet fighter and ofcourse faster than Mil Mi-27(helikopter) is in some seconds already gone.So the NEST team atack the Mi-24 and then from no where the Mig 29 comes back and starting attack them.
After this sceen it can be as in tf2,I mean that you see Sam at home,work, school and doing stuff.
If Thundercracker or Skywarp is in the third movie i think some of them should join the Autobot team at the end of the movie.
This is my begining of the movie