I think that current way: forum + launchpad cause less problems than in game bugtracker.
But the (general) idea is good. Maybe there is a way of improving it? But I guess that it would need more complex solution... I can imagine part of the server where you have bugtracker with open API for Widelands game. It means that we would have another copy of launchpad/ github here. Ok. It is possible, but is it worth it? I guess that there were more arguments for launchpad than for making a bugtracker here.