The Valkyrie is based on the 6.8 SPC, which was developed as a special purpose military cartridge (probably with hopes that it might see widespread adoption). Rather than adopt a new cartridge, I've read that the US military attempted to deal with the perceived shortcomings of the 5.56 by increasing bullet weight (77 gr Mk262, etc.). The Valkyrie would certainly make a decent military cartridge, by pushing those heavier bullets to higher velocities (or a 'general purpose' civilian cartridge, if a civilian owner was interested in that kind of performance).
Last I heard, the military was looking at 6.8mm again, with the 6.8x51mm/.277 SIG Fury being adopted on some sort of trial basis. It uses a three-piece cartridge case with stainless steel case head, and runs at some astronomical pressure level to reach the velocity they want in a .308-size cartridge. I guess you can buy a civilian-legal SIG chambered for it (for the price of a used car ;^), but a civilian can get similar performance with one of the existing .270 cartridges, for a lot less money.
I will probably build a Valkyrie if I stumble across a good barrel at the right price (I already have AR bolts & mags that will work). Or maybe buy one if Ruger makes an American rifle in the caliber (which I don't expect).
As always IMHO, FWIW, YMMV, etc.