I really like 4th and Niner's Idea about having a true minor league for the NFL. So I played around with it below. If you haven't read his post here it is:
https://www.cougarboard.com/board/message.html?id=23531277

I don't think the finances would work for having a minor league team for each NFL team. So I set it up so NFL teams, one from the AFC and NFC, share one minor league team. Somehow, the NFL teams place players on their minor league team. The two clubs work it out somehow. The minor league teams would also have free agents that any NFL team could pick up. Below is the list of cities with Minor league teams and the NFL teams that share them. Below that is the minor league divisions.

San Antonio - Dallas/ Houston
Richmond-Philadelphia/ Pittsburgh
Providence- NY Giants/NY Jets
Raleigh- Washington/Baltimore
St Louis- Green Bay/Cincinnati
Columbus -Chicago/Cleveland
Omaha- Detroit/Buffalo
Columbia, SC-Minnesota/ Indianapolis
Louisville - Atlanta/New England
Orlando- Tampa Bay/Miami
Memphis - Carolina/Tennessee
Birmingham- New Orleans/Jacksonville
San Diego - LA Rams/ LA Chargers
Salt Lake City- Arizona/Vegas Raiders
Boise - Seattle/Denver
Oklahoma City-San Francisco/Kansas City


Divisions

WEST - Boise, Salt Lake, San Diego, Oklahoma City

EAST - Providence, Richmond, Raleigh, Columbia SC

NORTH - Omaha, Columbus, St Louis, Louisville

SOUTH - San Antonio, Birmingham, Orlando, Memphis

This would be fun