why is XMPP shite? just look:

  <message from="juliet@example.com" to="romeo@example.net" xml:lang="en">
    <body>Art thou not Romeo, and a Montague?</body>
  </message>

69 chars just for the from/to. every. message. (more or less)

There is already a concept of session, why send the full ID? not just a short ID.

each byte costs energy, in this case most of the energy is spend on boilerplate, stuff that can be inferred much more cheaply.

Fortunately its not wrapped in HTTP, as that'd add even more boilerplate each transaction.