I've been doing this system for a while now and really love it. I assume I'll always go with it in all of my forthcoming dynasties. Promotion/relegation based on time zones. If a team goes winless in conference, they're out, being replaced with the best team from the corresponding Tier 2 conference or the Sun Belt. Tier 1's have 14 teams. Tier 2's have 12 teams (*correction - my MAC currently has 10). Sun Belt changes number of teams, at times, but typically has 7-8.
Eastern: Tier 1 - Big Ten (North), ACC (South) //// Tier 2 - American (North), MAC (South) All have North and South divisions.
Central: Tier 1 - Big 12 //// Tier 2 - C-USA Both have North and South divisions.
Mountain/Pacific (Combined): Tier 1 - PAC 12 //// Tier 2 - MWC. PAC 12 has Pacific and Mountain (the 6 or 7 teams closest to the Mountain Time Zone; some, at times, will technically be geographically located in the Pacific Time Zone) as its divisions*. MWC has North and South for its divisions.
SEC is also considered Tier 1, consisting of top Southeastern teams from from both Eastern and Central Time Zones, stopping at the conveniently placed state lines of North Carolina, Tennessee, Arkansas, and Oklahoma. Every state under, including Texas, can be included. Divisions are East and West, but could, of course, be changed to North/South, if more convenient. East/West has just always been more convenient for me, considering the shape of "the zone".
As it conveniently fits most of the remaining teams, like the SEC, I sort of treat the Sun Belt as it's own zone using this
map. Sun Belt can supply teams for both Tier 1's and Tier 2's.
Remaining teams are your Independents. For the vast majority of my dynasty they have been Kansas and Kansas State. Yep, the two teams smack dab in the middle.
* This is, of course, optional as you could always stick to the North/South divisions that work well, but I really like being able to let each time zone represent their own division since these two time zones are combined, sharing a conference.
For instance, I'm in 2068 in my current dynasty, and this is what my PAC 12 has grown into: Pacific - Nevada, UCLA, Stanford, USC, Washington, Hawai'i, Cal (and I know here you might think, "that's not much different than real life", but it's important to note that both UCLA and USC spent many years in the MWC, but were both able to make a comeback) & Mountain - Colorado, Air Force, BYU, Utah, Colorado State, New Mexico, Arizona
All of the maps and pics that I use:
Sun Belt Map
Time Zones
Geographical Team Locations