With the power creep we have now. I think they can just remove the hard mode option and bake them in for those base game dungeons.

We're talking about these six, right:
Spindleclutch 2: There's nothing extra hard here, the sacrifices are meaningless, there's never a reason to kill them. The most meaningless hardmode.

FG2: Not much harder, but requires some basic coordination and that darkness can hurt if you're really reckless..

Darkshade2: It is harder than not doing the HM, but most people don't know how to do the non-HM so nearly everyone ends up doing it anyway.

Wayrest2: Not really harder than the regular vet, the zombies are easy fodder, but if you do mess up you're stuck because you can't reset it.

COH2: Requires waiting for what seems like an eternity, but not too hard. If the group is underpowered they can kill some ghosts along the way. The only real issue is that the ghosts are so easy to kill, it's easy to get them all and accidentally kill them before the boss is properly pushed. If you notice it can be reset.

BC2: Like COH2 except the daedroths are much healthier, and more dangerous than the ghosrs. Hard to fail if you know what you need, but probably the most tedious for strong groups, and the most dangerous for low damage groups.

I don't think it would be hard to make a scroll and keep the mechanics mostly as is.
The last 2 could have the HM make the boss spawn directly with the required adds and make them invincible. The rest of the adds could keep spawning but not be invincible. Easy change. In theory the HM is supposed to be dealing with the adds, not controlling your cleave and being patient enough to wait it out.
Darkshade could disable the switch. No one would know.
Spindle could make the sacrifices invulnerable. Again, no one would know.
FG2 could just remove the shield.
Wayrest is the toughest to change because of the layout of the dungeon. You could make a bunch of zombies spawn when you start the fight on HM.