The SEC could use FSU,but not Miami.
Miami a private school would be a better fit for the B12 rather than the SEC.It would fit in well with Baylor and TCU.
Whether UT can keep two Florida schools out of the b12 if Fox wants them is another question.
Also the value in terms of tv dollars to the ACC is another question.
With the breakup of the old BE ND found a good new home at little cost to them.
You are right on Miami. In 1990, the SEC conversation with them did not go well. At the time, there was a big issue with the sports Miami sponsored at the time, particularly under-developed women's sports. Who rejected who may be argued, but it was no match, and Miami was showing some arrogance at the time, given their fb success during the period.
FSU was offered the SEC around '90, and opted for the ACC. I doubt FSU would reject an SEC offer now unless the ACC exit criteria forces otherwise. FSU has much more to offer than Miami.
When the SEC was saying they didn't want to add the 'second school(s)' from a state within, it was at the time of taking Texas A&M which had been in the works for years. For #14, Mizzou was suddenly making itself available, and frankly the SEC moved on the opportunity and saw it as the best option. The SEC could always add a couple of ACC schools later if they decided to, so FSU, Clemson, VPI were taken off the table for the prior expansion.
Miss. State, Ole Miss, SC, etc., may not be more opposed to expansion than any others in the conference. Some of these schools are in extrememly tight recruiting areas. Miss. State, for example, is in a comparatively rural region, has 'Bama just an hour away to one side, Ole Miss on the other, and also has to go against LSU, Arkansas, Auburn, and Tennessee for nearby prospects. Then add, Southern Miss., Memphis, UAB, etc., in the hunt, pickings are far from unlimited.
The SEC school that complained the most about expansion in '90 was Alabama. Georgia sponsored South Carolina. When Mizzou was added, 'Bama also rumbled about adding and divisions. Alabama is hardly a middle or low-level player when it comes to SEC sports. The most verbal (and active) Presidents on SEC expansion appear to have been from Florida and South Carolina. And their comments have not all-centered on FSU and Clemson critiques, which politically they cannot diss.
If the SEC expands, it would try to get into North Carolina. Perhaps Virginia also. And if Texas wanted in without unreasonable demands, I doubt that call would be unanswered. Perhaps Oklahoma as well. But the SEC would not want to take a new 'pair' from the same state, while having refused to take new additions from states within.
The "aces" for the SEC would maybe be among North Carolina, Virginia, Texas, Oklahoma, and suppose Notre Dame if such would ever be remotely considered. Most from the list would be unrealistic.
The SEC may have to take Duke (maybe NCSU) to get UNC IF the ACC unlikely breaks. A lot of issues with Duke football (stadium size, recent success, etc.) that are not so easy to accept. And, several other ACC schools would have to leave beforehand for that to be possible.