Let me preface this by saying that I don't discount that your scenario probably has been considered by the SEC and Greg Sankey. I also wouldn't discount the possibility that one day the Big Ten, ACC and Pac 12 might tell the SEC good luck and to go for it if they're feeling that strong.
That said, this idea of the SEC forming some "elite" super league in the 30 team range has a giant fatal flaw. That flaw is the current roster of SEC members. Those schools like Miss St, Ole ****, Arky, Vandy, Mizzou, Kentucky, South Carolina, etc. that would be grandfathered into an entity that we'd be told would be "NFL lite" but still would essentially be top heavy.
The SEC cultists would obviously continue their delusions about conference superiority from top to bottom but the sane remainder of the country would soon realize they're now just watching Ohio State vs Mizzou instead of Ohio State vs Iowa State or USC vs Vandy instead of USC vs Stanford.