Can't you just... Install the Epic Store separately from Google Play, like we already do with F-Droid?
Installing a store through Google Play sounds pretty stupid when you can easily just install any store's APK independently via the web browser.
They just need a way to let users grant that store the necessary permissions to install and manage apps, which currently requires root but is already doable. They just need to make a UI for it with plenty of warnings about the power this grants. F-Droid happily does its duties and updates my apps in the background and everything like it should, after flashing the privileged extension.
This seems intentionally done by Google to make it look more ridiculous than it needs to be. It doesn't need Google's involvement past adding a permission screen to Android, which is completely independent of Google Play. The ROM communities would get that done under a week most likely.