Well, I can see the Hogosha taking part in this sort of thing, definitely. They'd be paying the Kusari reps off.
IMG would be there, as it is effectively an independent littlle nation, as would the GMG. The Zoners might... it's unknown.
The Mollies would be there, sort of like what is going on with Israel and Palestine at Annapolis.
The Outcasts, I could see joining, saying 'We won't smuggle drugs if the following things can be assured...' They would then, after their assurances were met, smuggle drugs.
The Order would be represented, lambasting Liberty for having laboratories with live Nomad experiments.
The Corsairs might be there with a more pragmatic Elder. Arguments like 'The Order don't see our Artifacts as dangerous, so they should be legalised, which would cut our reliance on interdiction and privateering.' possibly showing up.
The Gaians would stand outside, handing out leaflets to the public, and maybe plotting to kill any Bretonian reps.
The SCRA would get an invite but laugh. They'd either not turn up or they'd bomb the proceedings.:P