Just considering partisan criteria, my guess is they need 12 Dem seats:
3 Dallas
3 Houston
3 Rio Grande/South TX
1 San Antonio
1 Austin
1 El Paso
I think they could get away with dismantling Fletcher's seat because Republicans are distributed pretty well in Houston and there's a lot of currently unused red territory (Brady's seat, etc.) nearby. In any case, Houston doesn't really need 4 Dem sinks, so if they decide to leave it in place they could probably keep it as a swing district and still protect everything else.
The GOP probably needs to concede a third seat in DFW unless they want to get very creative with rural areas; the geographic distribution isn't nearly as favorable there there. Austin is probably fine with one assuming the rest of the area is cracked.
The big wild card IMO is incumbent homes and priorities. 27 seats create a lot of opportunity for someone to be unhappy and could potentially mean additional Dem districts.
I increasingly don't think TX-39 is going to happen this round. How might things shake out differently with a 38 CD map?
Relative to a 39 seat map, my guess is that a GOP seat is lost in exchange for the others becoming marginally safer (could see this making a difference in Houston).
