Meh. By this logic, Canada & Australia doling out PRs should have been the beginning of the end for the US, and that hasn't happened.
Chances are the US will continue to attract the cream of the crop - for these folks, the 3 months they're given after graduation is usually plenty of time to find a job. While green cards may be a pain, it's easier to make top dollar in the US, there are far more jobs and you're more likely to have a higher standard of living than in Canada or the UK. The ones who don't find a job in 3 months usually attended sub-par universities, studied something worthless or the market didn't deem them competitive w.r.t their peers.
Back in the day, most folks who went to the UK to study did so because all they had to write was the IELTS (not the GRE) and it was easier to get into a program. Chances are the same bottom feeders will jump at this opportunity, setting UK up to be another country where a large number of immigrants are under employed or where they blow 2-3 yrs of additional living expenses before returning home.