The Lone Star Conference schools took a hard look at FCS after their numbers dwindle a few years back. Abilene Christian and Incarnate Word leaving put the conference in a hard spot.

Tarleton voiced their interest, has support from university brass, increased their athletic fee and is improving facilities while waiting for an invite.
West Texas A&M has a 20,000 person stadium already and is the lone athletic program in the Amarillo media market (250k population).
Texas A&M-Commerce has new facilities, history with Southland schools and recent success in LSC, growing quickly, and is located just outside of Dallas.

Anglelo State and Midwestern State looked at moves, but would likely only make the jump if the conference dissolved. While they currently have FCS-level facilities and are both located in cities with metro populations of more than 120k, neither really has an interest to move up.

Texas A&M Kingsville is the only odd one. Historically, they would seem like a no brainer for the Southland. 6 football National Titles, 16,000 stadium that is filled on a regular basis, just outside of Corpus Christi. However neither the school nor the existing FCS conferences seem interested in them.