I have to assume that the Big 10 is completely off limits. Otherwise, Illinois and Indiana have to be considered. Out of the easy to get additions, well most of them would not be the best additions (because after all if they're easy to get it might mean the strongest players don't want them). Also, while I think all things considered, the SEC got the best fits from the Big 12, I'd have to think the move to sure up the Big 12 means the SEC won't be hunting their programs anytime soon.
So, we're left with a handful of tough additions that would clearly better the SEC. If the SEC moves to 16, and doesn't get at least one of these programs I think the move to 16 would be linear at best.
1: Notre Dame - Arguably the most prestigious program there is. They are not that impressive on the football field as of late, but that's not a bad thing at all. Some people seem to think bringing in a program to beat up SEC programs is a good thing, it's not. You want to better the conference, not upset the apple cart. The fact that Notre Dame would likely struggle would only make the SEC look better, and if they didn't struggle? Well, if Notre Dame is winning they're raking in money. I don't like them, a lot of people don't, but it's the level of interest (love or hate), that makes them important.
2: Virginia - They make good money, they're the flagship university in the state, they enjoy good support of their football team, and perhaps most importantly they're not all that good at football. You add them, you get a lot of revenue and once again, you don't mess anything up to do it. Most importantly, it's a high population state that's not loaded with FBS programs.
3: North Carolina - A lot of the same can be said for North Carolina. Very good attendance figures, but still an easy win. However, their basketball program is stellar. This is offset a bit by the number of programs in the state. It's easier for TV sets in the state to be distracted, especially during football season, so it makes them a bit less of a consideration than Virginia.
Those three are all unrealistic, but they're also the only three that I'd say would be a clear improvement.
Then you get some schools that could be decent additions:
1: NC State - The thing about NC State, is that they earn really well. Their basketball program is one of the top financially, their athletic program is in good shape financially, and their attendance is football is pretty good as well (right about where Miami is, not bad for a basketball school in a basketball state). They're not North Carolina, and if you're making a TV deal you can bet that would be brought up.
2: Virginia Tech - The latter part says a lot, Tech. They've risen under Beamer, but don't forget this was a school even the ACC didn't want. Almost all of their value is tied up in success as a football program. Not a given in the SEC, so they could end up being a Miss. State in a bigger state. Not a bad addition though, but they also carry a risk in that the SEC is already brutal in terms of strength of schedule. They really don't need more football powers.
3: Florida St. - A lot of the same regarding Tech. Now that Bowden is gone, they find themselves in trouble financially. They're also made a bit redundant by Florida. But, Florida is a huge state, so if you're going to have two, that's the place to do it.
Honestly, I'm not sure I can go beyond that in terms of any additions that I think could actually help the SEC at all. Virtually any other addition would likely lessen the share of money to go around, so I just can't see the point. There are plenty of programs I like, such as Clemson, Louisville and so on, but would they even be worth a pro-rated increase in SEC payout? I'm not so sure.
I said most of this in another topic, but the SEC needs to be patient. If they don't add the right programs, don't add any.