It's a question of when, not if. And the only thing on the horizon that looks like it may ever surpass DS is 3DS.
I now think Wii won't pass PS2 though (but it will definitely pass PS1 and possibly GB). Part of that is that I really think we'll see a Wii successor a year sooner than PS2 did (Q4 2011), and the other half is that I doubt the Wii successor will bellyflop like PS2's did (and thus curtail sales sooner by actually transitioning it's base).







