Other than the cities already named by other posters, here’s more NBA expansion cities of the future:
Austin (growing like crazy these days, MLS team big success)
Cincinnati (old NBA city, missing NBA and NHL)
Havana (yes, Havana – tourist Mecca and old gambling mecca ready for big growth)
Hawaii (Honolulu – had a pro ABL franchise around 1960)
Kansas City (missing both an NBA and NHL franchise)
Louisville (old successful ABA city, likes roundball)
Nashville (growing like crazy these days)
Omaha (corporate headquarters city – sports fanatics town)
St. Louis (old legacy NBA city – sports crazy town; MLS team big success)
Tampa/St Pete (NHL very successful)
Austin won't happen with three teams already in Texas and any fans in that area are probably Spurs fans at this point.
Cincinnati and St. Louis have trouble supporting 2 teams. I don't know if they'd be able to support a 3rd.
Hawaii has as much of a chance of Alaska of getting an NBA team.
Kansas City needs an anchor for their arena but NHL seems more likely than NBA.
Louisville and Omaha are too small of markets to support an NBA team. Louisville's proximity to Indy prevents this as well.
Nashville is a growing city but it's way too soon for them to even entertain an NBA franchise.