It won't happen.
And any divison plan needs to have 12 teams.
ND won't ever join a conference.
The Big 10 already has 11 teams so taking in only one team would make it a 12-team conference.
As exciting as conference championship games are, I think they are actually a step backward from a college football playoff. When one of the main arguments against a playoff is that it would require schools to play too many games, adding a 12th regular season game and then adding a championship game on top of that - which often is a rematch of a regular season game - sort of bolsters that argument.
If there had been a serious attempt at a playoff system when everyone was playing 11 games no conference championships the argument against the playoffs wouldn't seem to hold water.