I'm going to say two generations(with each having either the third game or the sequels), one remake, three mystery dungeons(counting gates to infinity), one more Pokedex iteration, and three more spin off games(not counting mystery dungeon games).
I'm really optimistic about the 3DS's lifespan. I'd even say we might get more than what I mentioned.
In case of a Zombie Apocalypse, follow me! Add my 3DS FC: 2535-4356-9059 Name:Marcx