How would that work, even conceptually? I'm having trouble understanding what this would even mean. Only one account can make a post or a comment. The only way I can think where this might make sense is to change Lemmy itself so that an account is independent of an instance. Signing up for a second instance would "sync" your account to it. Viewing a user's profile might show all of the instances where the account lives. A post or comment author would be this multi-instance account. Wow, there would be so many issues to solve to do this, though. Moderation through blocking or defederation would become extremely difficult. And what would an accounts "username" be, given that the same handle may not be available on all instances?

That said, I think this tool is already pretty neat, even if it never attempts to solve the comment/post-syncing feature.