Dunno... You -can- actually get cases for PC's that incorporate everything (but the screen) into one unit. I couldn't find the page I saw these in, but they're out there..
Now, whether it would be a sucess or not, that I can't say.
If you look at portable computers today, they really -do- pretty much incorporate everything into one. And a lot of them come pretty close to being replacements for "desktop" computers, as they boast some very powerful components, CPU and graphics-wise at least.