A sticky point for me in Lemmy is that some instances are topic-oriented, and sometimes communities just seem to belong on a certain instance. For example, programming language related communities living on the programming.dev instance, which I recently discovered, seems to make good sense.
I registered for the instance and I enjoy being able to log into it and view the top local posts of the day, for example. Also if I wanted to create a community on that instance I believe I need an account there.
Anyway, it seems like there's a use case for one person having users on several instances. An issue with this is that it may be difficult to understand the actual identity of a user on a given instance, versus an impersonator. While I understand that there seem to be some partial solutions to this, such as linking to a website in one's profile which in turn validates the identity of various Lemmy accounts (assuming you trust the website), it seems like there might be a need for something more robust.
All this to say, have people already been putting thought into a system of identity that scales onto multiple instances? For example, what if you could send pairing requests between users across instances, where the requestor and requestee both must confirm that they are the same person and would like the accounts linked? Would ActivityPub be able to support implementing this kind of link?
Really I'm just wondering what the state of the art is on this kind of thinking... if any.
Maybe it's enough to have separate identifies where instances can choose to recognize OAuth or the like.