Xbox Play Anywhere is all about growing the ecosystem, and it does a good job of selling that IMO. Leave Xbox Streaming to cater for those who aren't willing to buy into the Windows universe, hook them with your exclusives, and sell them an OS that improves on the experience of playing those exclusives. Get a bit of money from those who won't budge, like iOS users who'll never buy a Windows tablet, while coaxing over those who can be coaxed like console gamers.
The extrapolated end to that though, to me, seems like the shrinking of Windows until perhaps one day MS doesn't even do Windows, potentially. Run your MS Office and Xbox games on your Mac or Google Something. That'd probably result in more money for MS than selling the OS, but there's no denying the change would be absolutely epic in the computing space. I'm not sure MS are willing to enter that possibility yet, and so I don't know that they can be looking at XB as being platform agnostic. Gaming is still their best driver for consumer PCs.