You are more than welcome to list your domains for sale as usual (Except in auctions forum) and add something like "Also Willing to trade for another domain" (Maybe add details about a domain you would accept in trade).
I don't think there's a need for a specific and isolated trading forum at this point though. Maybe if we see an influx of actual domain trade transactions happening via the method I mentioned above we can consider a forum just for it, however we want to make sure a forum can support itself in activity and not end up being a one thread per 1 to 3 month type scenario.
Eric Lyon