The SEC would have a scheduling and divisional mess if they went to 16. They could do the numbers OK, but identifying and protecting given cross division rivalries would be difficult and would require some member schools to make big compromises. At 16, the SEC would almost have to go to 9 conference games to have any kind of rotation with the other division or would have to decide to eliminate permanent cross-overs altogether. Such would also reduce the opportunities for some members to schedule P5 games OOC each year, and seeing more quality OOC games could diminish. Some members would have 10 P5 games anyway, but not with any new OOC P5 opponent. Expansion does narrow flexibility further.
That central core of Alabama, Auburn, Tennessee, and Georgia would be the schools most impacted with changes to cross-division rivalries, and that's even if they don't have to change divisions. If, for example, OU/OSU were added to the west, somebody has to go east with more complications.
Really, from a scheduling and marketing strategy standpoint, the SEC would do best to add one to the west and one to the east, and not move the exisiting. I'll say it, Texas. All can get over themselves. It's time expansion made more sense. The other, add NCSU to the east. No need to have 4 NC schools in the ACC. That would give the ACC a new market option, be it ND full-time (if ever happens), UConn, WVU, or Cincinnati. 16 could be reached from a combination within that group or find another not so obvious.
I believe the SEC will end up having a 9 game schedule whether they expand or not. The Pac and The Big 12 already play 9. The Big 10 is going to 9. That leaves the SEC and ACC as the only major conferences that don't play 9. Should they expand to 16 and split into 4 pods, which I believe is what will happen in the next round of expansion, you will see some sort of scheduling similar to the NFL. Play each team in your division or pod, 3 games, play all 4 teams in another pod, 4 games, then a permanent cross over rival from each of the other two pods. If a semifinal and a final are not allowed, then you take the two highest ranked teams from the 4 pods to determine a conference champion.
North- Mizzou, Tennessee, Vandy, Kentucky
East- Florida, Georgia, South Carolina, NC State
South- Auburn, Alabama, Ole Miss, Miss State
West- OU, AM, LSU, Arkansas
Hendu, you make a good point. That suggested pod model doesn't look bad. I expect with adding two teams, the SEC would seriously consider a pod arrangement instead of adding one to each division or adding two to one division and shifting a current school over to the other division. Since sixteen is generally considered the maximum target if there's further expansion, the SEC would be very strategic in picking what could be the very last two; or deciding on the premise that it would likely be for a very long time at least. They know they can hold back for the right ones and at the right time. That 9-conference games can be a touchy subject due to certain in-state rivalries that are OOC. Also, the SEC has some fussy schools about whom they play regularly, and that discussion, if it is to be fruitful, would require much give and take with pod considerations as well.
In the ACC, that Notre Dame scheduling rotation does complicate matters further.
There are indications OU spoke to the SEC recently. The SEC is not going to get itself tangled with potential lawsuits and GoR fallout. OU would have to be virtually clear of litigation issues before the SEC would deliver a formal invitation.
With recent ESPN financial questions and constraints developing, ESPN may not be in a generous mood concerning the development of the ACCN. And the B12, would find it difficult getting a conference network while the LHN remains outside that avenue, plus the question of how and where the conference would complement its current market.
Somewhere, somehow, there will be some focused implosion within the P5 that will create a limited catalyst for a few transitions with the P5. It may take a few more years.