My guess is that Louisville is going to get a home and home with Duke next year. It's part of the Welcome to the ACC Gift Basket. Syracuse and Pitt both got home games in football with FSU this past season. Louisville gets a home game with FSU in football this next season. Syracuse, Notre Dame and Pitt all had home games with Duke in basketball this season, with Syracuse getting the home and home. This didn't happen by accident. Because of the prominence of its basketball program, I expect that Louisville gets a home and home with Duke next season. The ACC will see what the ratings are on the Duke-Louisville games and the UNC-Louisville game before making any decision on new primary partners.
It would be tough to split up UNC and NCSU as primary partners so that UNC and Louisville could be primary partners. I have a real hard time seeing that happening. UNC wouldn't like it and NCSU would go ballistic. The ACC doesn't want to make any conference member as angry as NCSU would be if they were deprived of a home and home with UNC each season.
I suppose it's possible to go to three primary partners but ESPN would have to cough up some serious additional money to justify that kind of move. Everybody wants their home games with Duke, UNC, Syracuse and Louisville. Tie the power schools up playing more games with each other and there are fewer to go around for the other schools who need the big games to sell tickets and get on ESPN.