I don't think human nature will allow for the population transfers necessary to reverse the impending demographic collapse. In terms of skilled immigrants, it isn't really ethical to just skim skilled workers off of other countries without taking in some of their truly desperate people as well. We are probably at the very extreme end of the tails in terms of the diminishing returns from additional STEM skill-sets.
This is a major problem, and there is no fix on the horizon. See Japan for details.
http://ftalphaville.ft.com/2014/12/0...ns-demography/
http://ftalphaville.ft.com/2014/08/1...us-gdp-growth/