I think you can spin this however you like. Bottomline is that the Xbox brand loses strengh when majority, if not all of its big exclusives going forward are also offered on PC. That in and of itself will hurt those hooked in the Xbox ecosystem, not Windows, but Xbox (console only) ecosystem down the line. My guess is as soon as 2 years.
If the Xbox One were to be competing with a steam machine perhaps it's no big deal but it's competing with the PS4 and soon NX. You know marketing, and you know mind share....powerful drivers of sales. The stigma that Xbox doesn't have true exclusives will propagate and competitors will make sure to take advantage of the fact - it's after all, a differentiating factor. I mean it was 2 years ago wasn't it? Correct...
Does this change of approach by MS make someone's Xbox One stop from working? I don't think that needs to be stated. Obviously not. But for those whose only reason for keeping an Xbox One was one or two exclusives within a year have little reason to keep one vs. say a PS4 if he so happens to have a gaming PC. Obviously that market is only but a share, perhaps small, of the total Xbox One market. However, you start losing that share, you start losing folks that see the PS4 as a stronger brand due to perceived weakness in the Xbox brand, on top of existing advantages the PS4 has......it only reinforces one thing, Xbox's slowly but sure decline in adoption. MS will not lose third party support overnight, at the very least for this gen. That's at least the biggest sign of relief for those owning an Xbox One now. It will lose indies and some Japanese games, but they were losing them already soo...