I'm not 100% sure how the nba aprons work, but the second apron penalties restricting the ability to trade and losing out-year picks seem to have bite
Baseball will never have a hard cap, but I think MLB could realistically adjust to borrow some MLB ideas. I'd make a wage floor somehow tied to the average MLB rev share. If you don't hit it, you lose the difference between that average and your underpayment.
No salary "cap" but copy MLB in the idea of NBA apron. Once you reach a "cap", maybe current luxury tax, you get light penalties like minor haircut to international pool, beginning of luxury tax, some penaltiy on comp pics, limit on how much money you can take on in a trade. Then toss in a second cap that hits teams like Mets and Dodgers, where you take a real haircut on international pool, painful tax, loss of comp pic, requiring any trades to reduce your payroll. I'd let them sign any FA, but they couldn't easily eat an arbitration player from a small market club.
I think a salary floor would have to be target at more the bottom third of teas than just a look at Pirates and Marlins. You'd need a lot payrolls raising to make up for Mets, Dodgers having air taken out of their balloons and Yankees, Phillies being afraid of flirting with this line.