Cap for reasons stated above.
Other CBA wants:
Balance around the posting process for Japanese/Korean players. May be part of the cap or revenue-sharing calculation. Another area where large market teams (especially the Dodgers) dominate given the fees, and have an incentive to keep going to shut other teams out of the international revenue.
Service-time manipulation / Super 2 deterrents. Also related to the floor. This very likely has factored into our calculations the past couple of years. Fans want to see exciting young players promoted, and small-market teams in particular have reason to keep them down longer to save money and gain more control.