10-game conference schedule preserves all rivalries. 5 permanent / 5 rotating. You play every team in the league home and away every 4 years. You play 2/3 of the conference every season, still a smaller percentage than when 8 SEC games were played in a 12 team SEC. You get same number of home / away games every year.
Another option is a 10 game SEC schedule with a return to divisions. You play one permanent and 2 rotating from the opposite division.
Western Division: Texas, Oklahoma, Texas A&M, Missouri, LSU, Arkansas, MSU, Ole Miss
Eastern Division: Alabama, Auburn, Vandy, Kentucky, Tennessee, South Carolina, Georgia, Florida
Divisional format preserves just about historical rivalries by default.