While I agree, I think using e-mail as the base is an attempt to compensate for the network effect. While XMPP is clearly superior as a chat protocol, it lacks a broad user-base.
With e-mail you can even chat with people who don't have the chat app. Maybe we need an XMPP e-mail bridge ;-)
Btw, when I click "open source" link on delta chat website, I may be not the only one expecting to be taken to the source repository instead of definition of what open source is. I found the actual link, just a suggestion.
With e-mail you can even chat with people who don't have the chat app. Maybe we need an XMPP e-mail bridge ;-)