Chief among roadblocks is a locked bootloader on some phones. With it, no unofficial code will fly. (good for security, but bad for freedom and potentially bad for security if updates cease and community ROMs continue on)
Identical hardware will be kept apart by this. (See: HTC One M8 for Android or Windows)
After that, there's a matter of making Windows 10 Mobile be able to even talk to the hardware. While specs may seem the same superficially, there's a lot of differences on a low level that will have to be bridged.
There's just a lot of oddities to make it even work. Someone did get Android on a Lumia 52x though but it isn't exactly daily driver material.