This is going to be a fucking bonanza for a lot of places in the world.
There might be a little bit of a brain drain of natives from the US, although it'll be diluted and made more chaotic by a corresponding drain of people who really aren't that brainy but think they are. But I think the flood of people who used to come to the US to do their educational or scientific efforts, finding some other place in the world to go (or to flee to) instead, is going to really be pretty significant.