One thing is for sure. The power conferences won't expand just because people want the symmetry of 16*4 = 64. They would each need a financial incentive to expand. Adding teams just to get to 16 doesn't necessarily bring in more money.
There are only a few foreseeable near-term events that could cause another round of expansion. The most likely event is the disintegration of the Big 12, in which case the remaining four conferences would fight over who gets the valuable properties. I think it most likely in such a circumstance that the number of teams in the Power conferences would decrease by 6. There will be no effort by those four conferences to make sure everyone in the Big 12 has a new Power Conference Home.
Of course, as cable networks disintegrate, and ESPN gets ground up under the weight of its overpriced contracts (Quick! Shed a tear! ... Well, somebody has to weep for ESPN) who knows what will happen eight years from now. But it will still be about money. The conferences will only expand if it makes them more money. They won't expand for any other reason, and certainly not just to fulfill some arbitrary desire for 16-team conferences.