For that matter, should Dig/Fly and Psywave be made legal again? I don't recall the glitches with those moves being part of the pre-Crystal era, so if we're making a pre-Crystal mod Dig/Fly/Psywave could be lumped in with the changed mechanics.
Psywave I'm pretty sure it should be legal. I think that PP is the only place where desync glitches are taken into account (which is the case for the ban on Psywave), another simulators just mod it to never happen. Since it was the case for pre-Crystal era, I think there's no problem to mod it.
Fly/Dig could be allowed if invulnerability glitch is not implemented, but in this case, I have no opinion if this glitch should be present or not (RBYPlus uses this mechanic, that's the reason why you'll find a lot of Fly/Dig-like moves there).