Thinking about a new decentralized/serverless IM protocol

I'm thinking about a new decentralized/serverless IM protocol but
I don't want to reinvent the wheel so I'd like to base it on some
already working IM protocol.

The main goal of the protocol would be:
- no centralized user registry
- no centralized servers
- end-to-end cryptography & security

If you were to choose an IM protocol to base this new protocol, what
would be it?

Is there some IM protocols comparison where I can find some information
about problems of the current protocols to avoid them?
(A comparison of all the features of the protocols would be great!)

Since the protocol is serverless I'll need status to be polled from
every user (instead saving the status and having each buddy poll the
server)
What protocols are the most serverless?

I'm mainly asking for things to avoid and things to reuse.

If anyone knows references to some not centralized IM protocol it
would be appreciated.
(I already saw http://instantp2p.jxta.org/ but that still needs a
centralized user registry and my protocol won't need that)

Eduardo


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