so I wasn't sure how much local support each team received. If my memory is correct, I believe the UFL only had 4-6 teams which may have helped with the fan support. However, I thought at least 1-2 franchises relocated after the 1st or 2nd season, so maybe the support was only good instead of above average or great.

If the NFL were to start a development league/minor league, then I would think it would follow the NBA's path; specifically 1 minor league team is affiliated with 2 NFL teams. Given there would be 16 minor league teams, then it should increase the risk of misses on locations. Also, it may depend on whether the NFL wants the minor league's season to be in the Spring or Fall. I can see advantages and disadvantages to both.