A 14-team Big Ten is a scheduling headache. Even with 12 teams, Michigan is not seeing Wisconsin for four years (unless they meet in the championship game).
Currently, the Big Ten has static divisions and one protected cross-over game per team. The schedule rotates every two years, and every team plays eight games in the conference. If this remained the case, many rivalries wouldn't be contested in the regular season for 12 years.
The time lag could be halved, to six years, by adding a ninth conference game. But that still means that a player or fan wouldn't face the whole conference at least once, during the course of a four-year career.
The time lag could also be reduced by rotating the schedule annually, instead of every two years. But that means if Purdue comes in and beats you, you don't get the chance for revenge until many years later.
Another option is to eliminate protected rivalries, thereby increasing the inventory of games that can rotate every year or two. I am able to come up with only ONE static and reasonably-balanced divisional alignment that preserves all of the games that I believe the conference would feel MUST be played annually:
1) Michigan, Michigan State, Ohio, Purdue, Indiana, Northwestern, Illinois
2) Wisconsin, Minnesota, Iowa, Nebraska, Penn State, Maryland, Rutgers
This preserves Michigan-Ohio, Wisconsin-Minnesota, and every intra-state rivalry. With nine conference games, a team could face 13 out of 14 Big Ten teams at least twice within a four-year period, assuming the schedule rotates every two years, as it does now. Of course, this alignment, like the current divisions it is not geographical.
[Addendum: I assume most people know this, but Wisconsin-Minnesota is the oldest annually-contested rivalry in the FBS. Along with Michigan-Ohio and the various intra-state rivalries, it is considered indispensable. The Big Ten would never organize in such a way that those two teams skipped a year.]
Finally, the conference could align in pods, as follows:
A) Michigan, Michigan State, Ohio
B) Penn State, Maryland, Rutgers
C) Nebraska, Iowa, Illinois, Northwestern
D) Wisconsin, Minnesota, Indiana, Purdue
One of the three-team pods would be divisionally aligned with one of the four-team pods, and they'd swap every two years. In any given year, you'd play your entire division, and either two or three of the teams in the opposite division (depending on whether there's 8 or 9 conference games).
These divisions wouldn't be static (they'd change every two years), but over a four-year period everyone would play everyone in the conference at least twice. My guess is the league won't do something this radical, but as an out-of-the-box idea it's worth considering.