Another idea to help smooth out arbcom cases: Separate discussion of principles and facts from discussion of remedies. It stands to reason that principles and facts must be determined before remedies can be discussed, so making this more explicit might help. Once sufficient arbiters have voted on each point for the majority to be determined, and no new points have been added for 3 days (say), the principles and facts sections are closed the case moves into the "sentencing stage" (this could be done sooner with a Motion to Close if sufficient arbiters agree). I'm not sure if this would actually speed things up at all, but it would make it clearer that progress is being made.
(Of course, if the remedies don't take a significant amount of the time, this would be pointless - I'm not sure quite sure where cases are stalling.)