I think a stadium on campus would be better.
Mississippi State and ole miss used to use the stadium. Many times with both teams playing games on the same day. Their on-campus attendance is not much more than the Vets capacity. So, they could still be having games in the Vet. Yet, they moved their games back to campus. Why? I suspect for the atmosphere and ambiance. The experience of bringing alumni (and their children) back to campus, but, most importantly, money.
Newer stadiums are often multipurpose facilities - with classrooms, meeting rooms, and offices as a part of the structure. They are also revenue generators with skyboxes, seat licenses, and such. Considering the amount of money it would take to renovate the Vet and bring it up to modern standards while allowing JSU to fully utilize the facility, you might as well build on campus. Let JSU take their experience to campus and drive revenue from the facility on their own campus. Let the alumni and fans enjoy themselves while recruiting the next generation at home. On their own ground.
UMMC wants that land anyway.
Do this right and it could be a win-win for everyone.
Can't believe I'm saying this, but that's truly how I feel. lol