The vulnerability is in floppy drive emulator code. It isn't clear to me whether all users are vulnerable or only hosts that have floppy drive devices defined [in their guests] are vulnerable.
If the latter, perhaps Amazon was never vulnerable anyway?
If I were amazon, I would have done an audit of the hyperv software and removed the floppy driver code entirely if unused for precisely this reason. This strikes me as a basic, "no-brainer" hardening step for my billion dollar(s) hosting business.
Their PV domains are not affected anyway. Quite possibly they are running qemu in stub domains for HVM as well, rather than on dom0, but you may well be right about the floppy code too.
If the latter, perhaps Amazon was never vulnerable anyway?