Well, I think you're partly right, in the miniaturization, but I think that it's going to be more of a wireless/central computing application.
Picture a slim notepad, with a tactile keyboard, that's less than a quarter inch thick. The processing is done at some central server, to which you connect by wireless.
But that server is still going to be an "old fashioned" box, and unless the die traces get really small, it's not going to be any smaller than what it is today. PCs today are pretty much the same size, if not bigger, than they were 25 years ago.

When AT was replaced with ATX, we really didn't see any changes in size. uATX was nice though, maybe it'll pick up.
Right now, we've got 90 nm technology, and 60 and 40 is on the horizon, but it's getting real close to hitting some hard physics "wall".
If anything, watercooling could be integrated with the CPU. Kinda like my "CPU backside" cooler idea, but closer to the die. Then, that little pump might be just about ideal.