I think you could actually do that. You can run your own code, Apple doesn't actually care what you run if you have a dev account and are compiling your own stuff to put on your machine. So what's to stop you from installing an app store, or at least some semblance of one that would let you run your own apps under an app you compile and put on your iOS device?
I've never really thought about this before, but it seems like it's probably possible. Again, this doesn't help Epic -- they don't want to run apps on your phone, they want to monetize mass user phones, not give code to devs who are willing to put in the effort to install something through Xcode.
You just can't tell them how to curate the App Store.