I think by design of the ecosystem it makes the most sense for apps that can't be on the main store.

That would be emulators, uncensored social media, probably apps that do not meet the NSFW policy of the App Store... that kind of thing.

I'm not sure we'll see user-enabling apps for proprietary services like newpipe, because it's still a store, so corporate censorship is to be expected. In that sense, it is far inferior to a true, no store, side-loading ability like on Android, where you can freely install any application you want.

I've managed to get almost all my apps (sans Google apps and banking) to autoupdate through Obtainium on Android. It really feels like the future.