BC would bring some old skewl tradition into the conference, and IMO would be a great choice. Plus they'd offset the atrocious graduation rates the 'Canes.
Pitt wouldn't make any sense in terms of geography or money, but would make a whole shitload of sense in terms of turning the ACC into the best basketball and football conference in the country.
ACC has a while to go before being the best football conference. Three teams (maybe four next year if VT gets in) does not constitute a good conference.