Don't worry about the verboseness of XMPP - TLS with the deflate option drops that down to 10% of the original size. Or you can do what google did on Android and write your own binary protocol representation.
If I setup a new appleseed node and how do you really know it is me/example.com? I've yet to see that done well in http and would love to be proven wrong.
Which, if I'm not mistaken, is very similar to how XMPP does it.
The protocol also tries and minimizes the amount of actions that a third party node can take. You only trust your own node to take actions on your behalf.
If I setup a new appleseed node and how do you really know it is me/example.com? I've yet to see that done well in http and would love to be proven wrong.