What should the next chat app look like?

A single ID, identifying all your communications, is certainly not ideal: https://news.ycombinator.com/item?id=26998245

Why do we need another one?

What problem do you solve that wasn’t done with IRC like twenty years ago?

E2E encryption is the biggest one, but I'm not entirely sure it's worth the cost.

You're right that IRC is still better than most today. Two features I don't see addressed much:

Accessibility to non-techies and any device.

Portability and user ownership of accounts.

one without the keyboard