@sirjofri It depends on what you mean by an ActivityPub feature. Technically, the set of possible features is infinite, because every object property can represent a feature, and objects can have lots of them.
In my project I try to maintain minimal interoperability with all other services. So for me it works as a browser for social web, but it still doesn't support all features that other services have.
I think a universal reader app can be built. But not a universal writer. We should continue to build specialized clients for publishing different types of content, but let them connect to a single account.