California is already flooding into Texas, I expect economic diversification will come with it, along with a blue shift.
Texas isn't going to get more white and boomers will die off. So what republicans have to hope for is that gen x and younger suddenly change their minds and decide that gays are evil and that the rich need more tax cuts etc... not sure why they would do that in large numbers. There would also need to be a major shift on other issues like healthcare. Republicans are essentially taking the bad positions on almost every issue. People who are more connected with the world community know how full of shit they are because other countries have proven US republicans wrong on almost everything.
The only exception is probably abortion. I don't think there will be huge shifts either way on that unless a method is invented to prove the existence of souls and that they enter humans while in the womb.