I'm sure Disney has all the rights to NBC, and control of that property.  NBC was created by Burton while working for Disney, which is why Burton made the film for Disney, and why you won't find any of the characters outside Disney.  This is not that much different from Oswald, which was created by Disney.  Disney ended up creating Mickey Mouse, because of how he was being forced to sign a contract to take less money for each cartoon if he was to continue doing the cartoons.  This was blatantly unfair, because the character was very popular, so Disney had a right to expect more money for each Oswald cartoon, not less.  Roger Rabbit is a different matter.  Once Spielberg formed Dreamworks, Disney (I understand) was unable to work things out to bring Roger Rabbit to Florida, Hence "Mickey's Country Fair".  Disney would have a free hand recreating Halloween town at Disneyland, and your suggestion of using the space between the show buildings is an excellent one.  I actually think leaving the Mansion alone works better, then redoing the whole ride.  Expanding the grounds of the Mansion to incluude a larger area would be no more difficult then rebuilding one part of the Brick and Iron fence that surrounds the Mansion.  This could lead to a new gateway created, where you could either head tpward the Mansion, or through a graveyard that leads to Halloween Town (or whatever they want to call this land.)  It could include all the things you talked about, and open up the park some more.  The Mansion then would serve as a nice transitional part between New Orleans Square and the spooky area beyond the railroad berm.