KERA and KKXT are both Class C0 at the same height; however KERA is 29.7kw while KKXT is 19.3kw, so 90.1 is a somewhat better signal than 91.7, though it is not that much of a difference. Meanwhile WRR is a 98kw Class C, but a little over 200 feet lower for its antenna height. Overall 101.1 is the best signal.KKXT and KERA have about the same signal coverage. From a purely business standpoint, moving KERA to 101.1 and WRR to 90.1 probably makes better sense because KERA is the station that brings in the bulk of NTPB's revenue. 101.1 is a better signal than 90.1 and 91.7 are.
The Big A, however, is likely correct that the agreement with the city will likely not allow a move like that. We'll know more at some point as the terms of this deal will be public information.
I don’t see any frequency swaps happening in the 2020s. But I think that eventually The City of Dallas will quietly get tired of station ownership, even if it is being managed by an outside entity. Once we get into the 2030s I can see demographic preferences as well as technological advances in audio distribution forcing a change.
Another thought: As the Metroplex sprawls to the north, I suspect that the Classical music demographics may wind up living closer to the northern rimshots than to Cedar Hill. Perhaps the scuttled plan of 20 years ago to move WRR to 105.7 was just premature.