But what is the enforcement mechanism for SCOTUS to make the states repeal these laws if they indeed pass them?
When it comes to the federal government, the answer to "what are they gonna do about it?" is basically always "They're going to use violence." Bush and Obama both raided cannabis dispensaries in legal states.
Granted I'm not sure exactly what they'd target in this case and it would create even more public backlash, so maybe there's a chance that this change survives.