> You know that developers will end up using alternate App Stores

This keeps being stated as though it’s a foregone conclusion. All evidence points to the contrary. Look at Google Play. Android has allowed third-party stores since inception and yet the only stores that see any notable use are the ones that ship on devices, i.e. Google Play and to a much smaller extent OEM stores (at least in the English market).

So no, it is not likely that you will have to install another store. Just like most Android users only ever touch the Play Store most iOS users will only ever touch the App Store.

The only notable stores I expect to see from this are an Epic Games store that basically just has Fortnite on it, and some community-driven F-Droid-like.

What developers will do that? Android has alternate stores, and there isn't any vendor lock-in. The Amazon and Samsung Android alternatives to the Play Store aren't huge competitors. Epic hasn't tried to build their alternative Android app store yet with Fortnite as an exclusive. This is all scare-mongering about what could happen but probably won't happen. Name a single major Android app that's located on an alternative app store.