Do you have any links to this platform? There are already single-chip solutions out there to be had, but of course they all need at least some form of production-assembly to make boards. Sigmatel chips are used in products from popcorn Hour and SageTV among others for example. If you're going to roll your own software or install Myth's FE software, it's obviously a hinderance to rely on a single hardware vendor.

Will the solution you mention be close to the generic nature of current PC-building?

I can honestly say that I would not go back to a workstation-only solution. Client-Server is the most robust (and versatile) way to do the DVR/Media system as far as I'm concerned.