First, I have a question; where does it say 700 pokemon? And does that mean the regional will have 700? Or 700 pokemon are available in the game? Or is it just the number of pokemon will be over 700 now?
Anyways, I think finding a more diverse group of pokemon would be more enjoyable. I'd hate to see just mostly gen 4 & 5 pokemon, because they're "less annoying". Honestly, I don't even really like gen 5, so I don't prefer them anyways. However I wouldn't mind them being including equally just for diversity. It would be nice to have all areas include a vast number of pokemon so it seems like the place is thriving.
http://s253.photobucket.com/user/GuardianofAuraGirl/media/Anime/Pokemon/pokemon-019.jpg.html
I know it's a bit exaggerated, but for the most part, that's how I picture a sea full of pokemon. You know rather than being able to only catch a few options like earlier mentioned. Being reasonable, I know it'd never (or nowhere in the near future) be that vast, but its less tedious when you encounter 7 or 8 different pokemon rather than 2 or 3 in some cases.
Also, for those who say that the trailers could be post-game, come on. You can't really think that their first trailer would include post gameplay this early? (aside from Mewtwo, not sure if he'll be in the regional or not. Probably just for movie purposes) I think it's a possibility that not every pokemon we have seen is in the dex, but it seems likely since GF is very clever about their marketing strategies and they know how to tease the audience. I'm quite positive that these pokemon were probably hand picked because its strategic to put older pokemon in the first bits of promotional media.
Someone mentioned that these pokemon may have just been the ones to have their models completed. Unlikely, for us (the fan community) it is early, but for GF they didn't just come up with this idea when BW2 were launched. They had to have been brewing this early on, maybe even while BW2 development was happening. There's only one season left before October (summer!) and I doubt they're still finishing up models at this point. If anything they're working on finishing touches, perfecting things to their taste, making sure everything runs smooth. They don't work on the game right up until launch month.