Something which is inevitable. It's hard to turn back the clock on something like this and I don't see any obvious solution for it, which is why both companies need to be regulated heavily to ensure they treat app developers fairly. If they're going to monopolize their own platforms, then whoever wants to sell on that platform needs to have guarantees that they aren't arbitrarily banned and that they have sane avenues to dispute any conflicts with Google or Apple. This is what regulation is for, to ensure fair marketplaces.
Agreed, and it's not just app developers that would benefit from regulation, it's also billions of users. Consumers will benefit greatly from the increased efficiencies and lowered costs that real competition in the app distribution market will bring.