The big leagues need suckers too unless you want to get beat the hell up all year just to lose in the playoffs. But still, could you cut a few schools a replace with better ones?…absolutely.
Mississippi State is the 3rd smallest state in the P4 (behind Neb & WV) and is the #2 school in the state with the worst academics in the conference that isn’t on anybody’s travel wish list. The only thing they bring is a mid level rivalry with Ole Miss, a solid baseball program and a moderate sized football stadium that still only beats out a basketball school and a private school (I could make a similar post about Purdue in the Big Ten).
So let’s cut MSU (won’t happen but let say we can) you don’t want to replace them with FSU/Clemson. Already 50% of the conference has won a national title in the BCS/CFP era. The Big Ten and ACC are only at 17%, the Big 12 is at 0%. Those two only make sense if you expand to 20. FSU/Clemson solidify your base and shut out competition, while you also expand with a pair of lesser schools as well.
For a single addition you want a school that will bring new fans/eyeballs to the conference, potentially new markets for advertisers and recruiting, and other benefits like quality basketball, baseball, academics, or travel destinations for fans that also is contiguous to the current conference footprint.
That really only leaves 2 options. #1 North Carolina (or if they go North with the B1G, NCSU), and #2 Kansas.
Both have great basketball and as a result good sized fans bases despite lackluster football. Rivalry history with existing members, are good (not great) travel destinations in newish markets that grow the conference footprint, and both have unique color schemes and mascots (please no more red/near red colors or tigers in the SEC) and would slot somewhere into the lower half of the SEC hierarchy. While nobody would celebrate their addition to the football schedule but they would not morn the loss of MSU either and basketball would get a major boost.