Generations 2 (or something like it) was pretty much a given based on a picture they had shown off a while ago, except it also included Boom Sonic with them as well. I would enjoy the plot of this new one if it was Robotnik & Eggman teaming up through time again (which I am assuming is why there are two giant egg-mechs in the trailer) and having the two actually make an alternate time line where they take over the world and the two Sonic's need to work together again (and I feel like Boom will also be shoehorned in, guess he could be worked in as an alternate time line). It would certainly give the game a feel similar to the one Sonic cartoon/comics with the Resistance fighting against Robotnik's mechanical empire, something I wish the games would have tried to replicate at least once or twice.
I wish they would just push Modern Sonic off to the side for a while and make some new games (not counting Mania) with Classic as the main character again and with more simple plots and game play and classic styled zones/stages. They can be positioned in the Sonic "time line" sometime before Adventure 1 if people would give that much crap about it. Not saying Classic Sonic = game is automatically better, but I just think that bit more leverage or grounding that the character offers with the style of games he has been in is what the franchise needs for a while, to really get back to the roots instead of throwing anything against a wall and see what sticks.