Wine can run on aarch64 with FEX reasonably well already, no special instructions or hardware acceleration required. There's a bit of extra overhead, but that shouldn't be a problem for old games on modern hardware, they should run about as well.
Interesting, do you know if performance is roughly comparable with Rosetta 2, i.e., are we talking about a few percent of overhead or something more dramatic? (For CPU-bound code; I understand that the overall effect will be smaller due to GPU code probably being executed host-side in native code etc.)
FEX isn't done yet, but Valve's people seem to suggest an overhead between 10-20%. Not great for getting the most out of a CPU, but small enough to compensate say the difference between an M1 and an M5 chip.