Not really. The only time it would break is if Amazon moved Windows to hypervisor virtualization. When they're doing hardware virtualization, practically any OS should work and without much "kuldginess"
Colin's not suggesting some crazy hack, it's exactly the same as buying a Dell, formatting it to remove Windows, and then install BSD instead.
This is never going to happen though. Not because Windows PV is not possible. Windows was ported to Xen PV in the distant past because Cambridge University had a Windows source license.
The reason it's not going to happen is because with the latest chips and 64 bit, hardware full virtualization is faster than paravirt. Paravirt on x86-64 can't use the i386 segmentation trick, because x86-64 (long mode) doesn't have full support for segment registers. So it has to use some other trick which is slower.
Colin's not suggesting some crazy hack, it's exactly the same as buying a Dell, formatting it to remove Windows, and then install BSD instead.