If bringing down processing costs is the issue, Apple just did that.

Allowing multiple stores would increase costs doe small developers, because of the overhead of dealing with many stores and many sets of rules.

Any cost saving would disappear into one or two levels of middlemen, otherwise known as publishing companies.

I agree that the concept of a store within a store should exist for Epic and for users. I think “processing costs” is not really the issue. Apple’s revenue sharing business agreements just happen to be collected at processing time. They could easily invoice later. The core issue is: how much should Epic pay to have their own store on the iPhone?