I strongly suspect that if Apple win this case against Epic and get an official court-sanctioned nod that their monopoly on iOS software sales is acceptable we'll see developer fees double or triple within a couple of years and the 30% IAP fee get ratcheted up to 40 or 50% over the next decade (unless you're big enough to negotiate).

Developers would make a bit less (although still more than they make on Android) and Apple would make a lot more.