It’s not an English word. Its use here is most likely a misspelling of “shady”, which means disreputable, questionable, or possibly up to no good.

Was Elivis considered particularly versatile?

As I recall, Delta Chat is a front end for opportunistic PGP over email, so I guess this must be a spec for sharing web apps over that channel. Yes?

How does it compare to Matrix widgets?

In English, to dump is (usually) to unload or discard, so its use here is a bit strange. I thought I understood what was meant anyway, but I wasn’t sure.

“Dump”? Is that a literal translation of the Danish word for failure?

I don’t see a claim of it being more private than a username. Perhaps the person you’re arguing with views them as equally private, or is thinking of services that require some form of contact info. I can’t speak for them.

LOL what? No they’re not. How does an email protect your privacy over just a username?

They said per-account email addresses, presumably meaning that when giving out an email address, you would use a different one for each service. That way, they couldn’t be used to link you across services, and you could easily delete one (and know who to blame) if it was abused.