> Twitter's discovery is massively better

Do you mean recommendation algorithms, or just the number of users ie network effects?

> My "identity" was not portable between instances

Your identity isn't portable between email servers either. Or between HN and Reddit. Isn't that part of what Keybase is about?

I can imagine a couple ways of achieving this but it runs into a number of thorny issues regarding namespaces. Regardless of the approach taken truly portable identities would require lots of refactoring of lots of software in a FOSS ecosystem with fairly limited developer resources available.

Merely linking identities should be much easier but still each piece of software has to support it. Simpler just to link to your other accounts in your bio the same as on any other website.