It was never actually the unique "only we can do it!" option most Texans think it was/is. ANY State can secede, if they manage to jump through enough hoops.
Its highly unlikely to ever happen, though. Splitting a large state into two or more separate States is far more likely, but I doubt anyone reading this will live to see such a thing happening.
As a side note, Mexico doesn't need that kind of backhanded compliment.