Folks often think X and Y are on top and will be "forever", but we can look back 10-15 years and see that can't be expected. I think we can expect Ohio State to be near the top for a long time, but other programs have drifted off, and some will drift back, and some unknowns will get good. Remember Boise State? FSU? Miami? Of course.
I don't know if we've ever had a time in the last 50 years when so many BBs were down - USC, Texas, Nebraska. Bama has been on an impressive run obviously but that may wain in time post-S. UGA will probably stay pretty good for a while. Michigan may lapse into 9-4 ishness. Clemson? No idea really. Probably can win in the ACC.