How much potential is there for Fediverse frontends decoupled from a specific type of server?

I'm new to the Fediverse. So far I've been very impressed by the interoperability between the different instance types. Here in Kbin, I can subscribe to communities on Lemmy servers and have them seamlessly appear as magazines in the Kbin UI. I can also follow users on Mastadon servers and see all their posts as Microblogs.

It seems like the main limiting factor to this interoperability is the UI. Taking the example of following Mastodon users, the server has access to all of the posts made by the users I follow, but as far as I can tell, there's no way to view a combined feed of all the posts from the users I follow through the Kbin UI. Not a knock at Kbin or any other Fediverse server project. I know these are relatively small projects, usually running on donations and volunteer work.

On desktop, it seems like you're more or less stuck with the UI that's bundled with the server. On mobile, there are some third-party frontend apps popping up. Jerboa for Lemmy, Tusky for Mastodon, etc. There are also some projects that support multiple types of servers. For example, Fedilab claims to support Mastodon, Pleroma, Pixelfed, and Friendica. How far can that go? Could someone come along and make an app that supports Lemmy, Kbin, Mastodon, and Funkwhale, and simply gives you a different set of customizable widgets depending on the types of content your server supports? Failing that, could someone make a third-party frontend--either browser-based or standalone--that can be used to log into any Kbin server on desktop?

I'm interested in seeing how far this interoperability can go. It would be interesting to see headless Fediverse servers that rely exclusively on third-party frontends. Or a container mesh architecture for servers, so admins can pick and choose which containers to run to determine whether they want to host Kbin content, PeerTube content, Pixelfed content, or even slot in a separate third-party UI.

Are there any technical limitations that would prevent any of these things from happening? Am I making any bad assumptions here? Like I said, I'm new to the Fediverse, so I'm still learning about how it all works.