Hm. I could see that happening, potentially. But the thing is, the XB1 is completely locked down and under MS's control. The average Windows box has the OS, but the rest of it is completely outside MS's control, so they might not like that.
I think they're finally trying to push Windows as a game platform, again.
They realize people are doing it, anyway, why not garner some good will while DX12 is fresh? And maybe it'll turn into some extra sales along the way. If they can really get the Windows store to be a storefront for games, even if it's just casual games? It could mean MASSIVE money.
Where I'm interested is especially if they're serious about cross platform stuff. Though I can't imagine it will happen right away for any flagship titles. They've been so resistant to things like Halo getting to PC, for example. But, if multi-platform (probably third party) games that are already on PC/XBone... And the dev/publisher are both on board... And they can find a way to make the net code and infrastructure work... And they can find a way to get the control schemes equal... And a dozen other stars align... Who knows, anything's possible, I guess? It would be a major reversal of their stance for years and years.
It'll be interesting to watch, in any case. Phil Spencer really seems to be fully done cleaning up Don Mattrick's fallout from the XBone launch. This E3 was really good for them, the push for a reasonably priced OS... They've got some good will built up. It remains to be seen if they can really capitalize on all of it, but they're off to a good start.