The Sports Economist notes that the latest rule proposed by FIFA, limiting pro teams to a mix of 6+5 domestic and foreign players, would negatively impact Americans playing Europe. It would also lower the quality of play at home, since MLS would not be able to import more skilled players from the region and South America as it expands. Expansion will put more demand on the player pool, and lets face it, college soccer isn’t going to meet that demand by a long shot.
It is possible that soccer clubs would simply comply with the six plus five rule and keep on as they are. But lawsuits are sure to be filed by players who end up returning to a low-paying domestic league (think Irish, French, and Americans; this rule would also retard the development of players from the USA).