While LOLA is great, I'd really love an established handshake mechanism for having two accounts on two bespoke services represent the same user.
For example, I want to have a pixel fed and mastodon presence that can be authored between the two. However, you currently can't make two accounts that are effectively linked to each other. I feel like this linking is important for further decentralizing the fediverse (by effectively decentralizing the user itself)