There's a lot that has to happen for Texas State to move up.
They'd have to drastically expand Bobcat Stadium, and before that, make sure they could pull in the paying customers. I don't remember what the NCAA mandates as a minumum average attendance for football, but I'm pretty sure it's over twenty thousand, and I'm not sure Texas State (or SWT before) has even come close, including in Wacker's championship years.
It would take a lot of money, and while Texas State does have a significant alumni base, I'm not sure they have the kind of "got rocks" supporters to float the costs involved with moving up.
One more thing...what conference would they be in? The Sun Belt? That conference would have to be willing to take them, and there's no guarantee on that. I doubt they'd want to go the independant route...they're no Notre Dame.
One last thought...competitiveness. Texas State hasn't been very competitive where they're at for most of the last two decades or more. Mostly, they've been mid-pack in good years. What's going to magically happen if they move up that allows them to recruit the kinds of athletes that would make them competitive with the UNT's, Rice's, and SMU's, much less the big boys? I know they scared aggy a couple of years ago, but that was a one off deal where aggy just showed up.
Texas State would be a lot better off curbing the ambition, and concentrating on getting better where they're at. If they could become the Appy State of the southwest, that would be a significant improvement.