To this point in MLS history, intra-league moves involving star players have been fairly uncommon.
There are a number of factors that have made that type of transfer difficult to pull off. The biggest is probably that when a player establishes himself as a cut above in MLS, domestic teams that might be interested in him have not had the resources to match what is on offer from other, richer leagues, both from the selling club and the player’s perspective.
Clubs looking for a DP have tended to buy from abroad instead, where there is a much larger pool of players available to choose from.