JKR just said it will tour (I assume she's referring to a UK tour) and I agree, a Broadway production (as well as other international productions) are just a question of time. I'm interested to see what the reviews will be like, but first word of mouth was pretty good, and the run is sold out as far as tickets are sold out. This is as much a hit as Hamilton - in same ways even more so. They initially put 3 months on sale, added another 3 within an hour, and another 2 or so just another 1-2 hours later, and the entire contingent sold out, up to 1.5 years in advance, without even a cast announced, or any kind of word of mouth or reviews. Of course you can't really compare it because HP is an established brand and Hamilton wasn't. But it's still the same kind of commercial hit. It will run for a long time, and all over the world.
They might wait a bit before coming to Broadway I think. It's doing so well in London they might wait a while just my thought though. But as said above she did tweet to someone that a tour is being planned, so they might focus on that first