I seriously doubt that will ever become true. MS has quite some interests in them not becoming free software, that opening them might close some business chances currently being exploited.
I might buy that Windows could become free one day though, not to the extent of Linux however. Linux is not just free, it's open source. Giving the source and a proper license means that every customer becomes a potential competitor, and also able to view and modify Windows as he pleases. The outbreak of the GWX malware not so long ago shows how much MS loves secrecy, and the sheer amount of known spyware bundled into Windows 10 makes me think that they don't want that removed. Having it for free to anyone, maybe, open source....... I don't think so.
An example of this is the release of the DOS 1.0 source code
. Anyone can view and download it, but the license is still not free and nobody can legally modify it. That's as far as I think they could go.
About Skype, it also displays spam in the chat windows. Making it open source would mean anyone can clean that crapware, and even then, it still depends on a server component strictly under MS possession. It would not be 100% free either, and harms a way of getting income for MS: to steal user data and show them spam.
That said, it would be great if some day that becomes true. I don't think so, but would be a welcomed change.