With the present cpu/mobos reading memory to the standard of ddr3, making ddr5 on ddr3 sized strips would work perfectly well, but u firstly have the expense, and secondly there would be so much freedom wasted. Something to the effect of sticking ddr3 in a edo converter and putting it in pc66 setup.
My personal opinion is that 8 of these welded to a mobo, and something like a nb cooler put on them would negate the need for any memory for anything - until u need a new mobo.
Maybe not ddr5, but certainly ddr4, I'm sure AMD could build a mobo, with onboard graphics and a slot for a phenom. Small boxed sized games/all purpose pc I`ve been banging on for years they should build. Shared memory ? So what, u have the overhead as ur cpu can only access at ddr3 speeds at best.
Slimline bluray player/dvd rw, ethernet onboard, firewire, Realtek ALC889, loads of USB - job done. £400/500 easy.
EDIT: make that 2x onboard gpus.