the ACC, then I don't see why the ACC couldn't add 1 full member and 1 football-only member. There may be a problem with adding 2 full members because I am not sure the math works to ensure that each of the 17 members play a 20-game conference schedule. The math may not even work if the ACC decides to expand to 16 full members. The problem isn't with ensuring that 1 team plays the other members 1 time. The problem is with making sure all members play the same number of opponents a second time.

17 member ACC
16 games against each opponent 1 time
4 games against 4 opponent a second time

16 member ACC
15 games against each opponent 1 time
5 games against 5 opponents a second time

Can the ACC find a formula that will allow them to evenly divide up the 4 or 5 extra games among the 17 or 16 members? If the ACC wants to expand and keep the 20-game conference schedule in basketball, then the ACC may need to expand to 18 members.

17 games against each opponent 1 time
3 games against 3 opponents a second time

3 will divide evenly into 18 (18/3 = 6).