Apple could still be a gate-keeper of 3rd party stores. They could dictate the security and protections that need to be in-place to be listed. The PKI industry

Apple could still be a gate-keeper of 3rd party stores. They could dictate the security and protections that need to be in-place to be listed. The PKI industry is a good example of this. The Certificate authorities have to abide by standards and any misbehaving Certificate Authorities can be removed. I'd argue the integrity of the PKI industry is just as important, if not more so, than App Stores and they have managed to maintain a device agnostic market with healthy competition.