This seems a bit unlikely, but the Big East is, according to this guy, considering making a run at Maryland and, perhaps, B.C., as football schools. Obviously both would want to be full-time members, and the ACC would not likely be willing to split affiliations with another conference. So would the Big East expand to 18 on the basketball side? What would you do at that point - kick somebody out? That wouldn't do a lot to encourage the other schools.
Aside from everything else, there's a school of that that holds that the Big East cannot continue to be, essentially, two conferences.
How would the revenue splits work? And, not to be unkind to Maryland, but they're not really a football power, not consistently anyway. We're pretty sure that Gary Williams wouldn't be interested in such a move, and it seems unlikely that A.D. Debbie Yow would, either, or, for that matter, B.C. A.D. Gene DeFillippo, who put a lot of his credibility on the line to switch to the ACC (incidentally, the expansion teams are making a lot more money after the switch).
The natural fit for expansion, really for both conferences at least once upon a time, would have been Penn State. But that would be hard to pull off now.