The original thread dismissed a switch to Windows from Mac on basis of serious issues with Windows these days. Especially built-in surveillance and intentionally pissing off own user-base. Linux was never considered because, as of 2016, it's still a shitty desktop in all kinds of ways they just avoid fixing or are unable to:
http://linuxfonts.narod.ru/why.linux.is.not.ready.for.the.de...
Whereas Mac and Windows 7 are both great desktops that constantly polished stuff that users found to be a problem, steadily improved security, perform well, and have power-user features. Nowhere near customization or security I can with much effort get out of a Linux box. Yet, Windows (esp Windows Embedded) plus their admin tools show I wouldn't even need it if Linux had similar advantages. So, Linux is crap far as UX is concerned and that's intentional by many of its supporters or developers where UX is intrinsic to Mac and Windows platforms. Amiga, too, as MorphOS illustrates with way less resources than Linux desktops are getting. BeOS derivatives to a degree as the extremely-strapped Haiku is illustrating & its predecessor BeOS illustrated.
So, the baseline was Windows/Mac usability & ecosystem plus specific issues I mentioned in security & corporate character for recent Windows. Your next comment razor focused on open/closed source issue. My reply showed it didn't matter much since QA process and qualified reviews are what really count. Showed with evidence that OSS superiority for security was a myth since you brought that up next. Far as my concern, the lack of integrity of Microsoft or Apple means at least the TCB of system needs to be easy to inspect and enhance. Much of Mac is closed but I thought Darwin core was open and it supported many open-source, secure apps. Stronger position than Windows in this aspect.
So, we have two, usable desktops with one being more open and UNIX-like than the other. Makes little sense too switch away from the better one unless serious changes happen at Microsoft, Apple, or both. Also, one can always leverage secure virtualization or physical separation to get benefits of main OS for untrusted stuff with trusted stuff on FOSS OS. That one could be Linux but quality of most sucks. So, it would have to be one of most stable & reliable ones. I'd lean toward FreeBSD or OpenBSD with simplified, software stack for that, though.