If they're bringing Windows 10 to the Xbox One, then maybe they'll be turning the Xbox into just a windows PC but with no desktop access?
If that's the case, then perhaps their tools will allow developers who are making Xbox games to target PC at the same time with essentially no added effort other than adding k&m controls and exposing some graphics settings in a menu.
Instead of continuing Xbox as a platform, they can move to having just Windows be their platform, and Xbox will just become an entry-level device into their ecosystem. It would be a pretty bold and forward-thinking move that would protect their business model should consoles as they currently exist become less relevant as many suspect several years from now, but with no real detriment to the way in which they currently do business.
Imagine if Ubisoft no longer had to farm out their PC ports to Ubisoft Kiev, but instead all of the optimizations that they put into the xbox version of their games would also benefit people playing on PC since they would be running the exact same build, but with certain PC-specific toggles enabled.