That's a very good point. By 2030, for example, there is a good chance that North Carolina will be a "blue" state -- due to a large influx of relocated liberals from the Northeast. I would add states like Virginia and Nevada to that mix, too.
If you look at the statistics over time, Nevada has become more Republican with the influx, not less. The reason Harry Reid is a Senator from Nevada is as a deeply entrenched holdover from a decade or two ago when Nevada was a safe Democratic state. A significant majority of the immigrants to the Mountain West identify themselves as Republican, a higher percentage than the native population of those states. It has only been in the last ten or fifteen years that Nevada has started converting all its Democrat seats into Republican ones.
Of course, many of the old Nevada Democrats were more conservative than today's New England Republicans...
The only complication with states like Nevada is that they strongly lean toward small-L libertarianism in political philosophy, more of a Goldwater conservatism. They are very uncomfortable with the Republican-flavored socialism popular on the Eastern portion of the party -- they want less government period, not more. Most of the rest of the Mountain West leans the same way as well to one extent or another. If the Republicans don't manage this, it will eventually be the undoing of the party. The populations of the Mountain West states now hover firmly around the median for the country, and therefore (along with their natural allies like Alaska) have not insubstantial political clout in Congress and particularly in the Senate.