I don't know if Disney would want to go through the expense of changing the ride its self, however, your idea of a dark land on the other side of the berm could b created through the ride waiting area.  In NBC Jack entered Halloween town through a crypt.  It may be possible to reestablish the 1969 Graveyard, which would lead to a crypt that would get you beyond the berm, and the space between the HM Show building and the POTC Show building.  The architecture of Halloween Town, could be used to create the shop and restaurant area, and possibly Jack's slay ride, or something regarding Disney Villians could take place there.