18 would be either Notre Dame or a team from the east. There aren't any other western teams with a sufficient footprint and AAU or close to AAU membership. Remember, the AAU research money completely dwarfs the football money. It matters to the B1G a lot.
The target list for the B1G is actually really short, because each school must add to the contractual footprint, be in a state with one or more major media markets (or many mid levels), not be in a state already added or being added, and be AAU or close: Texas, Notre Dame, Oklahoma (possible, not a lock due to AAU), Kansas, Virginia, North Carolina OR Duke (not both), Georgia Tech.
There has been some noise that Florida State is an outside possibility, but I don't see it.
Delaney also wants states that add to the future demographics (hence huge interest on his part in the VA, UNC, GA Tech combo), and the B1G prefers to be contiguous with no gaps between states.
If I was a betting man, I'd say the most likely next four are VA, UNC, GA Tech, and Kansas. Don't worry about the much-ballyhooed Grant of Rights agreements. I've worked in contracts and procurement all my career, and trust me when I say no contract is ironclad. There is always a way.