Twitter implementation seems good enough. Big display name with smaller unique handle below. Might be a bit bloat, but solves the problem.

His concern is probably that in comments etc. only username is displayed. You have to go to person’s profile to discover their instance.

There are far more important things for lemmy devs to focus on. Security is one of them.

Yes, instances share data. It’s called federation. Nice intro to how all this works: https://github.com/amirzaidi/lemmy