I really don't think it needs an IP, just a revised story and some new scenes - Squiggs' vision a page or so back would fit the area and existing facade so well and wouldn't resort to an IP.
While I do agree with you that Squiggs' concept is good and all, I think many people seem to miss the point on what the building and style have in common, lack of storytelling. I think that what the ride lacks now is what makes the haunting feel ever more present, fear of the unknown. What is there to fear when you know what's going on around you thanks to heavy dialogue and visual storytelling. Only young children would be frightened.
To me, less is more, visually and Story wise. I still believe that reverting back to what it used to be is the best route for its first few seasons.
I'm not against his idea as a whole though, I really like some of the ideas he thought of, especially the finale scene being a dense forest instead of a Swamp. These could be great ideas if they wanted to change the ride ever so slightly over time if they brought it back to its original form and intent, like Knoebels Haunted Mansion, which also has had its few shares if scenes and scares coming and going over its years. Duel/HH still has very important history to the park, present or not.
The ride still has a very unique style thanks to its theatrical portrayal when compared to other Haunted Attractions, and should not be ignored for something new for the sake of it. The ride is like a Jigsaw puzzle, it all comes together very well when everything is put in right.
I'm all up with change, but i think its best if they did it gradual, start with the Haunted House how it looked back in its heyday, and over time, like a good 15-20 years, make it into Squiggs idea. Go with John's plan, give it something new every once in a while, that ranging from a year to 3 if they wanted.
The problem with all this, both sides on this discussion, is execution.
I doubt that Merlin would do a good job retheming it to Squiggs idea, or it reverting to its former self, because we all know that Merlin will somehow screw it up for profit and budget cuts. The only old ride in the park they properly respect is Nemesis, and everything else from that period is just a distant memory, long forgotten. the only people I trust altering that ride are the Ops and Hosts (pathetic, isn’t it) John himself, and former workers of Sparks and Rex, heck, even people who are just really passionate of the ride. Literally anyone but Merlin.