Ah, looks like they created a much lower-power TETRA in a different band for North American use (search for "low power tetra"):
https://www.powertrunk.com/pressroom/tetra-in-north-america/
That's cool, but it's going to be a niche use at those power levels. One of the things that make TETRA and P.25 so attractive is that you can put a huge, high-power repeater on a hill or tall building and cover a big chunk of a city using (fairly) small low-power handsets. Then multiple agencies (police, fire, spooks, clowns) can all use that repeater and share the cost burden.
The power-limited version looks like it'll always be a fairly niche single-agency-in-single-jurisdiction use. So the threat, while technically not zero, is not at the five-alarm-fire level that it is in Europe.
Edit: also looks like MTA bought their own spectrum license just for this one use:
MTA owns licenses in 700 MHz and 800 MHz
