And there's a perfectly suitable extension to D3D for this approach: quad buffer stereo. Maybe framelock extensions, too - there are developers who would positively kill to have those features in D3D. It is actually rumoured that QBS will be the next "big" feature for D3D12, but (a) that's a couple of years away and (b) there's a whole new market emerging here (new 120Hz HDTVs, 3d Bluray etc).
The window of opportunity is here, any takers?
(I'm only half-joking. Wouldn't it be awesome to beat Microsoft in their own game?)