It's real hard to make grandiose predictions about what's going to happen to the ACC when they won't even start talking about it for a decade.
If it were me, I'd invite the 6 Pacs (Oregon, Washington, Arizona, Arizona State, Colorado, Utah) and Gonzaga and Creighton as non-football members (1/8th share each). I'd give Oregon and Washington the freedom to negotiate with the Big 10 as they see fit while reaping the rewards of having them in the league while you can in exchange for a slightly reduced share that is still more than they'll get staying where they are with the full understanding that they're eventually headed for the Big 10 with no hard feelings.
When those two leave during the next round of moves, you'll still have a perfectly viable 16 team football/18 team all sports league that would give you some flexibility if someone jumped up over the next half decade.
Stanford and Cal to the Big West with football independence or football only with the Mountain West and, well, sorry about that Wazzu and Oregon State, we still love you but it's not you, it's me.