Yes i've been to the Haunted Mansion Holiday, I use to live 30 minutes from Disneyland. It's still re-decorating and using stationary animatronics. Not too different to stick an animatronic zombie and throw additional dead body parts around the Jurrasic Park ride, as well as local speakers playing additional scream effects/music (which might be a cool idea to make Jurrasic Park have a Halloween theme to it).
The whole Simpsons ride IS the movie and the synchronization of the ride - both of which are highly involved and time consuming processes that you don't give enough credit to. Its like reprogramming Star Tours at Disneyland or Back to the Future. If it was so easy and worth the investment, I think they would have been done to said rides to keep the rides fresh rather than bore the audience with 10-15 year old entertainment. Due to the time and cost of doing this, I doubt they will anytime soon or just for HHN. I'd guess they would in the next 5-10 years once the popularity of the ride dies down. It seems that people like the Simpsons ride but get over its dizzying effects after a handful of times on the ride.
Don't get me wrong, I would be stoaked to see this happen and the Treehouse of Horror episodes are some of my favorite. But from seeing rides like this programmed in the past, I'm just not convinced it will be worth the investment... yet.