Presumably that would be combined with an x86 JIT, though I've been baffled for years that WINE doesn't already include that for non-x86 architectures...
(There would also be whatever software was written for Windows NT 3.51 and 4.0 on PowerPC, but I don't know that there was ever much of that.)
darwine has included a x86 emulator for years... or you could just use wine with the qemu userspace emulation layer.