I don't think the Sunbelt needs to do anything so drastic as to expand to 16. Especially with the 4 schools being FCS upgrades and WAC schools.
The Sunbelt could very well expand to 12/14 with a pair such as LA Tech and NMSU or UTSA & Texas St. Just adding a pair would help them out. Based on the current footprint, the conference might be better off with UTSA and Texas St and solidify their spot as the #3 conference in Texas behind the B12 and CUSA. Who knows, maybe UTSA and Texas St. grow and one day the trifeca including North Texas might challenge CUSA.
But La Tech and NMSU don't add too much to the SB. But it would hurt the WAC. But then again, taking the 2 schools the WAC really needs to survive (UTSA/Tex St) would accomplish the same.
I agree that the Sunbelt does not need to do anything right at this point, but if they wanted to have geographically consolidated divisions, then I think my proposal would satisfy all existing members. However, I also would not be surprised if the Sunbelt waited patiently to see how emerging programs like Ga St. and UTSA do before committing to them. With 10 members they can afford to be a little patient, but you can never be too careful, just ask the WAC.
Once the Ga. St. program gets going, and if they upgrade to FBS, having them in the Sunbelt seems like a no brainer to me