Since we are in the fediverse, I think it would be convenient to have a fediverse-wide resolvable fediverse URI scheme, that would look like so:
fediverse://
edit: Found a relevant FEP: https://codeberg.org/fediverse/fep/src/branch/main/fep/07d7/fep-07d7.md
Okay, sure you could have apps open links to external posts, as the app would know that it would need to fetch the post by searching the URL (switched with a HTTPS scheme). I can kinda see the point of that. I’m not sure the fediverse and ActivityPub is really super mature enough for that yet. For instance you can’t fetch Mastodon posts from Lemmy.
Having a standard URL scheme would precisely help us develop ActivityPub clients and get rid of application-specific servers.
Doesn’t change the fact that Lemmy does not support posts outside of communities.