Even though it's been open for just a couple of weeks, I can pretty confidently say Runaway Railway will not be considered "sacred" someday. However, I would agree the castles are iconic and sacred as icons of the park - especially when you look at what they are doing to Hong Kong - perfect example of change that is NOT better. Yikes.
I would also say Epcot's "ball" is iconic and sacred, but I'm open to a new, great attraction inside it (again, confidence is very low they can deliver on that idea).
But that list of truly sacred icons and attractions in the park to me is very small - from the 11 years Walt ran Disneyland and his plans for the future (which is all we have to go by) he wanted the park to be new, fresh, exciting, and tell the next story with his next great set of tools. The original ppl Tomorrowland barely lasted 10 years before he tore it down and started over.
As I've said in other threads, I think Walt would be horrified if he came back and found out the Carousel of Progress that he debuted in 1964 as a symbol of modern technology and storytelling was still being run in 2020 - it's exactly the opposite of what the show stands for - progress. (And this is from someone who LOVED it from the day it debuted at Disneyland)
To quote Pippin, "Everything has its season, everything has its time...."