I could imagine some sort of scheme where home versions are free to download, but the right to redistribute is not included in that license. So OEMs still have to pay for an OEM version, and the server version still costs money.
But that would only work if it's legally possible to open source even that much of it in the first place, which may not be the case.
So the OEMs would Instead install a Linux bootstrap system that gets online and then downloads+installs Windows on behalf of the user.
Linux distros already do exactly that for other “open source but non-redistributable” things Microsoft offers, like the MS Core Fonts. The distros’ packages for the fonts don’t contain the fonts, but rather a wizard that goes and gets them from Microsoft’s servers on behalf of the user, and then installs them.
This seems legitimate enough, as an approach; nobody’s ever been sued for this. So I’m not sure there would be much difference in the legality of it if it were the whole OS.
> So the OEMs would Instead install a Linux bootstrap system that gets online and then downloads+installs Windows on behalf of the user.
I doubt it. That kind of first-time user experience would probably do more $ worth of damage to the company's reputation and sales than what OEM licensing costs.
Linux vendors may be able to do it just fine, but Linux PC vendors cater to a very different target market from Windows PC vendors.
But that would only work if it's legally possible to open source even that much of it in the first place, which may not be the case.