It would be great to be able to link an account on one instance to another instance elsewhere on the fediverse. A way for there to be an “official” recognition that the human behind the one account controls the other account, without the clunky system of having to put the link in each others bios.
To me I feel there are 2 separate uses of the fediverse: creation or consumption. Consumption is technically universal, I can use any fediverse account to follow any other account (with some software exceptions that you pointed out). Creation of content needs to be done on local accounts (at least right now). To create a top level post on a Lemmy community, you need a Lemmy account. Same thing when uploading a video on a Peertube instance. Hence my suggestion for a way to properly link accounts across the fediverse. That way it’s easier to “verify” that the account that uploaded videos on tilvids.com is the same person that posts it on lemmy.ml