That is an interesting idea, because it starts with the obvious, which many who do not know ACC history well ignore: there are some games that must be played annually or else there is a great risk the conference will come apart. If we have moveable division save for 3 i each division, as you have it, we have a good start toward becoming flexible. UNC-UVA is The South's Oldest Rivalry and must remain annual. UNC-Dook and UNC-MooU also must remain annual, as must MooU-Wake and UVA-VT. So, if we have the six permanent teams and they each have an annul cross-divisional rival (UNC-MooU, UVA-VT, Dook-Wake) we have knocked many of the required annual games.
Other games that are annual musts: FSU-Miami, FSU-Clemson, GT-Dook, GT-Clemson. I doubt any of those schools will go along with any change that would not keep the annual games they most want.