You can probably build a computer, especially if you reduce its
functionality (limited interface options, only one RAM-type etc.) but:
Who will write software for it?
Who writes the BIOS, the OS (preemptive multitasking of course...), the
hardware drivers, the programming languages
Who writes applications? Mail & news. Webbrowsing. Utilities. To name
only a few essential
What about games? Can they really compete with modern games on the PC
or will we see the usual assortment of Tetris, Minefield & Breakout?
And what about backward compatibility? I can see the people forming a
lynchmob because they want nearly complete (*insert your favourite
machine here*)-compatibility/emulation.
So where are the armies of programmers that actually want to spend
money and/or time on a system which does not have commercial relevance?
When I see what happens with the Power-Amiga platform I can guess how
much success it would have - though they already have a clean & modern
hardware and a multitasking OS.
Sorry for being pessimistic.