In an 18 team conference playing 8 conference games, the pod system can be built that 3 undefeated teams can not happen.
A theoretical 24 team conference playing 10 games meets the same standard. And that's where it's heading.
I'll take your word for it (that a system could be constructed that would eliminate the theoretical possibility of 3 undefeated teams emerging), but that is not what the Big10-18 (with a 9-game schedule) has developed. If you would like examples, I'll provide them. (Its a non-trivial amount of work, so i'll only do so upon request).
At the risk of a threadjack - an 18 team conference can assign teams to 6 pods, and essentially create a 9 team division out of those that changes every year. The 9th game could preserve an unprotected rivalry. They chose another route, and I found one 3x undefeated possibility in about 30 seconds because the Illinois, Indiana, and Iowa do not play each other at all. Same for Michigan St, Minnesota, and Northwestern. I guess that's what NBC paid to get.