there's very little indication that academics (AAU status) is playing a significant role in this stuff.
thus, i really doubt that the B1G is interested in picking up GT, stanford or cal at this time. duke and uva, maybe. duke has an elite basketball program for sure, but football is the driver here.
and i don't believe that the SEC is remotely interested in any of SMU, louisville or VT.
will any of those schools eventually make it into the top @ 50 schools mega conference fold? probably. but there is no incentive for the B1G or SEC to add a bunch of schools with middling football programs / athletic departments at this time.