I have just read online that besides the new multi-stairwell addition is not just the only new effect coming unique to WDW's mansion. It was reported by Screamscape that there will be a brand new shadow and footstep effects added to this mansion not seen in any other versions of the ride. This site is also mentioning those other additions that many sites are reporting:
The list of new effects being added includes replacing the old Leota, a bit of work in the Ballroom scene, all new Graveyard props and a new bride in the attic. (I’m guessing this may be the same Black Widow bride added to Disneyland about a year ago.) Apparently they’ve also installed a couple of brand new shadow and footstep effects not seen anywhere else yet that has made the Disneyland crews jealous.