My answer to OP's question is quite simple. If suburban shifts were to continue to the point of TX becoming Dem-leaning, that would also mean Arizona and Georgia being more solidly Dem-leaning, which would mean the GOP having no possible coalition to coming even close to victory presidentially. Which would mean some sort of shift in voter coalitions would have to occur- and it is very difficult to envisage any such coalition which would involve Texas being to the left of the US as a whole.
If the parties realigned along economic left/social right vs economic right/social left, it's possible to see the parties trading some of their core states. Dems gain Texas but shed VA, MD, NJ, CT perhaps.
