I imagine some of the resistance to an 8-team CFP would be because of the potential for a P4 scenario in a few years when the Big 12 GoR expires. In that case, the remaining power conferences could arrange for de facto autobids to a 4-team CFP for their champs, and going to 8 teams would be unnecessary.

However, an 8-team playoff could actually work for a P4 scenario without dropping CCGs. Perhaps if CCGs and divisions were deregulated, each P4 conference could hold two "championship semifinals" between their top 4 teams, with the winners automatically advancing to the CFP. So the P4 conferences effectively get a double CCG payout on top of the increased CFP payout, even though no conference champions are actually crowned. This would also necessitate only one extra week of games, an easier sell than the two extra needed for an 8-team CFP plus a 2-round conference championship.