Statistically, nobody actually builds real UWP apps, so it is largely an academic point. But if you're out of the sandbox, I fail to see a good reason not to just build a regular old Win32 app the way it has always been done.
If you are on Windows on ARM then there is no option other than UWP apps. Why would anyone buy an ARM laptop if they have to rely on emulation for everything anyway. It's not like the ARM laptops are any cheaper than the intel ones. (they actually have worse specs and cost more)