MLB said the same city teams will not be in the same division. That's a really good decision if you want to maximize baseball interest in large markets (which they absolutely want to do).
I wouldn't be surprised to see San Antonio get an expansion team. I would make that division Astros, Rangers, SA, Royals.
So much of this depends on which cities bid for expansion teams. I expect bids from San Antonio, Nashville, Charlotte, Portland and Salt Lake City.