Well, I think it's certainly going to be more possible. Devices will get more powerful and more complex.

At the same time, when I think of the BEST uses of these devices, it's not to replicate entire MMORPGs. I think we have to remember that these things are on the go devices and as such I really feel what will benefit the player more would be more supplemental software. Even if a full on 3D MMORPG was possible and ran perfectly, I don't think it would really be using the platform for its true strengths... Particularly given how little time most people would use them by comparison (ie, I play my DS in short bursts and my consoles for hours).

Of course, this is just my opinion.