Story comes out: Notre Dame to ACC? This is ND &/or ESPN pulling the strings - hey, B1G, you might miss out on having 'US'.
Rutgers & UConn to ACC - TV's & Basketball (not just football) at play. When Syracuse & Pitt to ACC was announced, whose quotes were first posted on the additions? - Coach K @ Duke
Add KU to your conference, it immediately makes it more relevant on the basketball landscape. Mizzou would add quite a bit in both basketball & football. Both help cement two whole states.
ISU would be probably somewhere in between Mizzou & KU - with the exception of TV sets. Geographically and academically would be a great fit, but lack of additional TV market is largest hurdle. I don't think KSU can be included unless KU says both of us or neither of us (but I don't think KU's position is such that they can take that strong of stance).
In the end, if add ND, then adding ISU becomes more palatable (if the likes of Mizzou & KU round out the 4)