@blendergeek From what I can tell:
Coreboot is ok with windows.
Libreboot on purpose does not boot windows (for people’s own sake).
@SeVaS I see where your question is coming from. I had a similar question. But after I found out more about Qubes OS I realized that it’s much better than a SATA switch I was thinking about. Qubes OS is even better than dual booting, since you can create a disposable VM with Windows on it and “burn it” 
after you are done playing a game or using an app or smth. And then have another permanent VM with PureOS on it for all the other things. No bottom lines for now, just sharing my journey to freedom and the point to which I got. 