The LA times article had a pretty extensive list of the changes they are making for this refurb. On the whole, it all seems positive. Mostly minor stuff to add to the ambience and general mystery of the attraction. They talk about the April/December addition, minor changes to the drapes, some new flooring in the foyer, a new floating chair in Madame' Leota's room, a new prop or two (including a dollhouse) for the attic, along with the new foliage and a new pet headstone or two outside.
I don't think we'll see much more than that. Nothing at the level that folks are worried about.
That all seems very positive, to me and I'm sure it will look great. The only (very minor) worries I have are over the line about them possibly removing the skeleton from the stretching room (a problem which admittedly, has not happened yet) and with the new temp looking wall across from April/December. I'm sure it'll look nicer in person, I just hope that it doesn't obscure too much of our view of the "boundless realm" loading area. During normal Mansion it's not an issue but during Holiday, I don't think it's a good idea to try and obscure the wonderful advent calendar from Guests in line. Maybe it'll be a non-issue, I haven't seen it for myself yet!
In any case, with any change, the positive side of it means that if they're willing to adjust or update anything; it means they plan on keeping it long term. I'd certainly hate to lose Mansion in my lifetime. Any future changes just assuage my fears of that happening.