I think we may have this backwards. In 4-5 year stretches, hasn't the top 4 always been populated by the same few teams? If there's fatigue now, why any more than in the past? If we went to 8 teams - guess what? We'd have a larger handful of the same teams making the playoffs even more often. The random, "down" year by Bama (10-2) would yield a playoff spot with 8 teams. The larger the playoff, the more familiar faces there will be.
Regular season end, Top 4 rankings
4-year stretches, with 2-year overlap:
2012-15
ND, Bama, Florida, Oregon
FSU, Auburn, Bama, MSU
Bama, Oregon, FSU, OSU
Clemson, Bama, MSU, OU.............Bama 4, Oregon 2, MSU 2, FSU 2
2010-2013
Auburn, Oregon, TCU, Stanford
LSU, Bama, OK St, Stanford
ND, Bama, Florida, Oregon
FSU, Auburn, Bama, MSU...............Bama 3, Stanford 2, Oregon 2
2008-2012
OU, Florida, Texas, Bama
Bama, Texas, Cinci, TCU
Auburn, Oregon, TCU, Stanford
LSU, Bama, OK St, Stanford............Bama 3, Texas 2, Stanford 2, TCU 2
2006-2009
OSU, Florida, Michigan, LSU
OSU, LSU, Va Tech, OU
OU, Florida, Texas, Bama
Bama, Texas, Cinci, TCU............OSU 2, Bama 2, LSU 2, Florida 2, Texas 2, OU 2
2004-2007
USC, OU, Auburn, Texas
USC, Texas, Penn St, OSU
OSU, Florida, Michigan, LSU
OSU, LSU, Va Tech, OU..............OSU 3, OU 2, LSU 2, Texas 2
Pretty consistent, no? The teams cycle through a bit, but there's always a handful who peak in these stretches....