It would be a signal that MS is throwing in the towel as far as Windows as a separate OS. However, I suspect they already have some kind of Windows compatibility layer of their own that they’ve been working on. It would probably have some sort of limited source availability, as opposed to a full open source FOSS licence. If that is the case, it could actually undermine WINE. If MS could save face somehow and fully embrace Linux, they might do it, but I doubt it will happen. Who knows.