It is obvious, at one point the pool of guys who have 1500 hours will be dry. And at that point there are only three options for the US:
1. change the law, although this will be difficult since in the public perception this law has made aviation safer
2. stop expanding, compensate with less dense networks but bigger planes, which takes a lot of time and destroys a lot of value in the enormous RJ fleets of the US
3. tweak with immigration bureaucracy and bring foreigners in who speak good english, fit culturally and probably already hold FAA papers