If ND agreed to join, I'd reach out to Maryland and see if they'd beg to come back. If not, I would just see if three five team divisions would work (I need to work out the math). No need to force a 16th team into the mix especially one that would add nothing to basketball (like Navy).
BUT by bringing in Navy, you get
A) a service academy and we all know how the ACC likes to tout academics,
B) one of the old ND rivals that ND isn't going to give up (so that would become an annual conference game,
C) the DC/Baltimore TV market which UMd was supposed to deliver and
D) the ability to divide into 4 pods *-
Atlantic Division being North Pod (ND, Navy, 'Cuse, BC), Mid-Atlantic Pod (VT, UVa, Pitt, 'Ville), and the
Coastal Division being: Carolina Pod (UNC, State, WF, Duke), South Pod (Miami, FSU, Clemson, GT).
*Each team would play the other 3 teams in their pod, plus 2 of the other 4 teams in the other pods. Longest you would go without playing a team is 2 years so no more of this 8 years without playing teams in our own conference. This would also guarantee that, for recruiting and exposure, each team would always be in one of the pod areas. This would also requiring going to 9 conference games vs 8 though. I'm good with giving up a "powerhouse" team in basketball when it gives other areas. How many basketball schools does the ACC need?