I'm yet to see how regulators would react with such a move. If they didn't allow Facebook to proceed with the Libra/Diem project, what makes you think they will allow stablecoins to have their own chain? By doing so, Tether and Circle would become centralized financial institutions (more like banks). All subject to FinCEN laws in the US and whatnot. I'd "stick" with truly-decentralized stablecoins (eg: DAI) just to be safe. I mean, they're also risky but at least they're not subject to the likes of corporate entities. We'll see what happens in the long run.
There is a new law for stablecoins, and these companies certainly have legal advisors who know what they're doing. The situation is completely different from what it was during the Libra/Diem project.
Generally, these companies were able to freeze tokens, and they did it across multiple blockchains. However, there has been no freeze on individual addresses, and this appears to be the next step.