Given that this is a rule rather than a law, what would it take for (e.g.) DeSantis to put the kibosh on it in 2024?
I am not 100% sure of exactly the process once the rule is posted to the federal register.
For it to be an executive function, I suppose the President could order the ATF to come up with a new rule undoing this. The new rule then it would have to go thorough the rule-making process (Notice of proposed change, public comment period, updated proposed rule, wait time, publish to register)
This should more correctly be a legislative function, but the legislature has had decision paralysis for years and seems unlikely to recover any time soon.
The rule could be challenged in court, but unlike the frame and receiver rule I suspect the ATF is correct in their analysis that most of the pistol braces sold "redesign" the pistol to be fired from the shoulder, and the SBR definition (unlike the frame and receiver definition) is spelled out in the relevant legislation. I think we'd have better luck challenging SBR's inclusion in the NFA itself under Miller (weapons that have a reasonable relationship to the effectiveness of a well-regulated militia ... are free from government regulation.) and/or Heller (weapons in common use are protected) and that's probably a long shot.