re: Once the playoffs expand, what SEC teams will constantly be in?

None. No teams will be consistently in. That's the point of the SEC.

Too many teams ... the Big 6 ... that, when hungry, can get really good really quick. And too hard to prevent complacency - as Smart and Saban say publicly.

But that's the secret sauce of the SEC. It'll be two or three different teams every year. On a rotating cycle.