Won't happen. We simply don't need the pilots, the US has the strongest GA scene on earth and plenty of pilots coming up through the ranks.
The regionals aren't hurting for pilots because there aren't any, it's because their pay doesn't match the job description, and not one chit is given for their cheap arses.
I'd also imagine the airline unions and lobbyists would block a airline from brining in foreign pilots who are willing to work for peanuts, just to keep from having to pay a proper wage for a US citizen regional pilot.