DSi system wouldn't cut it because it cannot play Gameboy/Gameboy Color games. I'm not sure if DSi even plays Gameboy Advance games. That might have just been the hardware removing the slot for the cartridges, but they might not be able to play them even if they did have the slot. I just don't see the business sense of releasing a system with the sole purpose of playing old games.
I still think Pokemon is great. Although I do agree that adding Mega to a Pokemon's name is pretty lazy.
If they were permanent evolutions I would totally agree. It would have been a lazy way to add fourth evolutions for certain Pokemon. However, I like the fact it is meant to be a battle item. It only takes affects during the battle. Leftovers doesn't allow you to heal your Pokemon outside of battle while walking aroung (my god that would be amazing/broken). I've read a theory that the Pokemon chosen have a theme of the Norse Gods. That theme is already being hinted at for the game as all the games have some sort of inspiration for its legendaries, location, story, etc. If all the Mega-Pokemon are connected through a common theme that is pretty spiffy. If not, opportunity missed. Until I see the Mega-Pokemon in action, it will simply be a new held item for battles. Nothing more.