thats my thought, i bet it would be a very busy sub forum, busier than say the pike cichlid forum... loads of us keep betta, not necessarily an anabantoid but betta!-)
I sent up a req for a possible Mini-Monsters subforum. Keep in mind that it may go the way of many other forums the site used to have. No traffic will get it merged back to one of the existing sub-forums.
I won't recommend a betta forum. We used to have an anabantoid forum here that was active for only about 2 weeks with bettas, gouramies, and climbing perch. Then, nothing. It got merged back to Other Monster Fish.