Guys...
Could this be huge?
http://www.windowscentral.com/micro...ows-android-smartphones-run-windows-10-phones
At least there will be no need to wait for a Ms flagship device
Nope, not huge. Installing custom ROMs isn't something your average user can do. Even if there was no problem with firmware and drivers, the impact of such an effort would be negligible. Actually, even if at the time of purchase the customers could freely choose between the default OS and another choice, they'd still all go with the default, because it's the default, and they don't know/care enough to make up their own mind.
The only impact such a program would have is, that enthusiasts could go out and buy some high-end Android phone to use Windows on. That would be convenient, since no one is making high-end Windows Phones.