It really doesn't matter. Disney is not going to build another domestic park. The infrastructure costs would be prohibitive. WDW has plenty of land for another park and the overhead is already established with park management, hotel management, transit management and more, all of which would need to be recreated as well as the physical infrastructure of a new park. And new parks need to open with enough attractions to make it a stand alone experience. An added park at WDW does not need to be a full day experience. The openings of, at the time MGM, and AK show that Disney knows additive parks can be done with fewer attractions and then built over time. A new stand alone would be prohibitively expensive to replicate a full-day park, and opening a half day park between Houston and San Antonio has no business case in the Disney method.
Location isn't really important so long as you can fly for a few hundred dollars a ticket. Orlando thrives on tourist tickets and that's why there are so many budget carriers in and out. Until you reach that kind of critical mass in another area, the flights tend to be more expensive and less convenient. While making Houston/San Antonio a massive tourist hub would cause the flights to follow, from the get-go they wouldn't be available, dropping the customer base. Disney needs fly-in tourists to cover costs. The AP holders are the cheapest customers. Per day they spend less on tickets, souvenirs, food and lodging then fly-in guests. So you aren't going to build a park in Texas for people within a 4 hour drive. Yes, you need those people, but they aren't your real money makers.
I understand the desire, and fully agree that the Houston/San Antonio corridor would make more sense than anywhere else in the U.S., but any logical examination of the business case very quickly shows that it will not happen the way things are right now. No one can predict 40 or 50 years down the line, of course, so things may change. But looking at any kind of 2 or 3 decade plan it is plain the numbers simply do not come close to working.