Which extremely red/blue state will become a new swing state?

[pbrower2a]

I'm going out on a limb on this one,  but I'm going to say Idaho because

(1) it has a small population
(2) it is attracting high-tech businesses that require people who generally lean D
(3) it is likely to get a huge influx of Mexican-Americans
(4) the importance of farming and ranching as a share of the economy is likely to decline.

This is the sort of state whose demographics can change rapidly. It seems reasonably pleasant and has plenty of high-quality recreation. Boise is about as warm in the winter as St. Louis, but without the  heavy rains and snows... remember that cold rains are even nastier than snow upon you You can brush off or shake off snow, but you can't brush off or shake off rain. Summers are cooler on the average than those in Grand Rapids, which isn't too bad -- except that it is a "dry heat", which makes it more pleasant. Extreme highs are close to those of Dallas, but... Dallas is a growing city or urban area, too, As in Dallas, "it's a dry heat". 

Double the population and Idaho becomes much like Colorado in the Double-Zero  Decade or Arizona now in politics.