Similar cap rules to what we have now (exceptions, minimum contracts, Bord Rights, etc.), but no max contracts. A superstar like Lebron should be getting paid way more than a barely-max player like Al Horford, but the rules don't let that happen (and no, supermax contracts do not solve that). If OKC wanted to sign KD for something like $35 million, they should have been able to. Teams that manage the cap well and have lots of cap room, or draft/trade well to get the Bird Rights of superstars, should be rewarded by being able to offer them whatever they want. Luxury tax would still be a thing, so teams would still need to be careful, but there would be way fewer super teams if guys like Lebron and Durant had to give up legitimate amounts of money (like $10 million or $20 million a year instead of a few million over 4 years)
Of course, this will never happen, because it takes money directly from 90% of NBA players and gives it to superstars instead. A lesser version of this would be to keep maxes how they are and increase minimum/exception/rookie salaries significantly, making a team with a few maxes and then all traditionally cheap contracts more expensive, but that would just move money from the "middle class" of NBA players to the lower end, which is similarly unlikely to happen.