Most FIRE people aren't going to have $50 million plus and be hit by this.

It will never stop at $50M. Once the law is created it is sooo much easier to just lower the threshold. Even if not lowered, in 30 years inflation means it will capture a whole different number of people - maybe you. Maybe it will bankrupt your children.

30 years is plenty of time to change the law. We change the tax code all the time. In 2020 or so it was recently amended to substantially increase the standard deduction. Slippery slope is a fallacy unless you can prove the pattern already exists.