A Dallas-Houston rivalry would be good for the NHL.
The only league where Dallas and Houston don't share a division is the NFL. For TV reasons, the NFL can't do a purely geographical alignment like the NBA and NHL. That's why there's the AFC (in which Houston plays) and the NFC (in which Dallas plays). As such, only 2 Cowboys-Texans regular season games are guaranteed to occur in an 8-year period, in which they always meet in years divisible evenly by 2 but not by 4. They could meet in years divisible by 4 if they finish in the same position within their divisions the year before (as they did in 2024).
There has never been a Dallas-Houston rivalry in top-level professional hockey. WHA only ever had Houston, and the NHL has only ever had Dallas.
Dallas and Houston (and for that matter, Fort Worth) did co-exist in the first version of the Central Hockey League, starting in 1967-68 and ending in 1968-69, and again starting in 1979-80 and ending in 1981-82.