I really disagree that it adds replayability. Souls games always had tons of it. And, at least in my opinion, the large majority of it came exactly from the brilliant level design and how you deal with it in future playthroughs.
Most of what makes me keep replaying Dark Souls is the fact that my initial 80 hours playthrough is now barely 5 because I know the level design, I can now clear the Catacombs running for a few seconds and rolling twice, I can clear Anor Londo in a couple of minutes without fighting any mobs, this kind of thing is a big part of why I love those games so much, the dungeon changing every time I play goes against that.
Again, it's one optional dungeon, so I don't mind, but I can't agree with this vision (that From Software themselves seem to share) that it's this kind of thing that will keep people playing for years. Dark Souls didn't have it, people are still playing it. It's not about "every time being like the first time", it's the exact opposite, having a completely different experience by knowing exactly how the game works.
Rushing to the Solaire Bonfire in Anor Londo, running up the stairs, turning back, jumping and landing right in front of the O&S fog wall? This kind of shit is amazing.