I'd be happy if they split into two divisions of 16 (as mentioned),
however, arrange it more like baseball.
Have two separate balanced schedules
and the Cup would be between the two division winners.
The reason it likely would not happen is MLS wants to maximize the promotional opportunities.
Let's say LA was awesome and had big name stars, then the league would want LA to play in as many places as possible
rather than just the 16 teams in their division.
But my counter argument would be that the league has grown enough to succeed in that situation.