When New York F.C. takes to the field, MLS will be fielding 20 clubs. That's enough for four five-team divisions.
So, is this a good idea?
Well, the MLB, NHL and NBA currently have six divisions, and the 32-team NFL has eight.
However, most other premier leagues around the world don't have divisions at all, including the English Premier League, which also has 20 teams.
However, most other worldwide leagues have a smaller geographic footprint than the MLS (usually only one or two time zones instead of four), and many also have fewer than 20 teams. Though some of these leagues (including the EPL) play a double-round-robin regular-season schedule, other leagues have unbalanced schedules.
And how would the divisions ultimately line up?
Well, for starters, one team is going to have to move from the East to the West. Houston and Kansas City are the most likely targets for movement. I'd move the Dynamo to the West so it could be in the same division as its Texas derby rival Dallas.
Dividing the MLS is complicated by the fact that the MLS has a different geographical distribution than the "Big Four" leagues. With six teams on the west coast, the Whitecaps will have to be in a different division than the Galaxy or Chivas.
The MLS also isn't fielding a team in the Southeast right now, and only fields three teams in the Midwestern United States. By contrast, the MLB and NFL are each fielding nine teams in the Midwest, and the NBA is fielding six teams in the southeast.
Assuming mostly geographically distributed divisions (i.e. nothing like the AL/NL or AFC/NFC dichotomy, no "zipper"), here's what I perceive to be the only feasible scenario for a four-division MLS:
New York City F.C.
I know that these might not be the first divisions that come to mind, but on closer examination, they make a lot of sense, if for no other reason that they preserve many of the MLS' clásicos.
Start with the Atlantic Division. You have Red Bulls and their traditional rivals in the Revolution and D.C. United, plus their future Big Apple stablemates and Philadelphia because it fits in geographically. Looks almost like the NBA's Atlantic Division, except with Washington instead of Toronto.
Obviously, things look a little different in the West in that it's divided north-south instead of east-west. However, this way preserves the most rivalries: you've got a Northwest Division consisting of the Rocky Mountain and Cascadia Cups. It looks very much like the NBA's Northwest Division did from 2004-08, but with Vancouver instead of Minnesota.
As for the Southwest Division, you have the Honda SuperClasico, the Texas derby and the California Clásico. It consolidates most of the MLS' large Hispanic markets in a single division, and shares four markets each with the current AL West and the final incarnation of the NHL Pacific (no teams in Phoenix or Seattle).
But, as you may have guessed, the Central Division is where it gets wacky. Composed of the five teams that couldn't find a place in the other divisions, its two farthest members (Montreal and Kansas City) are separated by over 1,300 miles. Only one clásico exists between these five teams: the Trillium Cup between Columbus and Toronto.
Frankly, the Central Division alone is enough of a reason not to have divisions in the MLS.
Bottom line: Because of what the Central Division would end up looking like, and because most Premier Leagues operate without divisions, I don't believe splitting into four divisions will be necessary for the MLS at this time.