University of Missouri and Tulsa (City/University) have recently opened arenas as well. Tulsa's is an 18k event center, I believe, and is part of their overall downtown revitalization scheme.
The city of Tulsa is building a new downtown arena, in the neighborhood of 18,000 seats. The University of Tulsa built a new facility in the 1990's, the Reynolds Center. It holds around 8,000.
I do not expect them to move all of their games downtown, but they very well may play a major opponent there from time to time. This new arena also makes Tulsa a player for NCAA regionals and Big XII tournaments, similar to OKC.
They do not quite have the market size for a major league franchise, however. Oklahoma City is borderline in that regard (would be the smallest TV market in the NBA, right behind Memphis), but is doing well as temporary host of the Hornets.