you can easily "encode" contact info in messages.
I understand the reasoning for enforcing to be the middle man in the transaction but the real purpose of such a platform should be the guarantees. And in that case, it makes no difference knowing or not knowing the other party. You would want audiogon to be the broker and pay the fees happily to have a safe transaction and a smooth process.
People from this forum hooking up to meet in person is not a threat to their profit.