The owners aren't going to get a salary cap unless they're ready to give up a loottttttt of concessions. Which, given the general bastard nature of baseball owners, likely won't happen. But I think the players would agree to a salary cap if the following criteria is met:
1. A salary floor accompanies the cap, and a high floor, like $130m.
2. Both the cap and floor are tied to revenue as a percentage, around 50%.
3. Young players either make a lot more money (such as arbitration after year one) or reach free agency earlier.
Do those things, and I think the players would accept a salary cap. The problem there is that the owners absolutely will not agree to those things, as the players make more money under that arrangement, probably a lot more.