Well Serebii has a 7th generation page, with Magearna and the little bird shown in wireframe imagery from the Sun/Moon trailer. So, I'm thinking it's generation 7. It took me a while to realize that generation 6 debuted in 2013. So when Sun/Moon drops, it would be 3 years since gen 6 game on. Long enough for that generation to be born and gestate. If I'm not mistaken, gen 5 was 2010 to 2013, gen 4 was 2007-2010 maybe I guess. Basically it's around 3 years, so yeah. By then the XYZ anime could be done, and if a new season comes up that ties into Sun and Moon, it further proves it to be generation 7. So that's the easy prediction.
The grander, more fantasy based one, would be that it allows for a Kanto post-game, featuring a new area, or hell, Safari Zone in Kanto replaced by something like gen 4. Pal Park. There, you can get the RBY transfers. Maybe even span all the regions, but the games are supposed to be for all 3DS models, such an adventure sounds like something for the New 3DS. I could be mistaken though. As for Solrock and Lunatone, maybe, I never really thought of them being front and center. It could be that they're keys to access a cave that houses the mascot legendary, who are also based on the sun and the moon. Maybe bust out more dragons. Fire/Dragon legendary and a Water/Dragon.
More megas for sure, hopefully all other starter pokemon getting covered. Hell, this would facilitate a 2017 release for Diamond and Pearl remakes, you get the Sinnoh Starters getting Mega Evolutions. A new mechanic will be added. I don't know, three types, fusions, a new battle type, something.
Whatever happens, I am definitely excited, I'll pre-order the games and everything.