When do you think Texas could possibly flip? Shortly after Georgia does?
Well, there's really no way to determine exactly when a state "flips." You can really only go by Presidential elections every four years. And trends can get in the way. You could say that California flipped in 1988, even though it didn't vote D until 1992.
And I don't think Texas or Georgia will ever completely flip. Neither one will ever be blue states, as the strains of social and economic conservatism are just too strong to be completely overpowered. But I do think both will become swing states. Georgia could become a majority/minority state by 2020, and when that happens we will have definitely flipped.
Texas is already majority/minority, but a flip will depend on higher Hispanic turnout and keeping them in the D column. Stronger growth in liberal cities like Austin could also speed up the process. It might also help Democrats if the economy continues to diversity and is no longer dominated by the conservative oil and gas industry.
But you have to remember, Texas is a state that Clinton never flipped, was won by Bush with well over 60% in 2000 and 2004, and Obama lost by about 10 points. It will take a while for demographic trends to overcome that legacy, so probably more than 10-15 years. But it can happen, I mean look at California.
Well, the fact that 6 of the last 8 elections included a Texan on the Republican ticket probably helpped steer it into the blue states.