Some ideas:
Amethyst items: Possibly will be added underground.
Copper: The mods recipes will be merged with the vanilla copper.
Azalea: Should spawn in jungles, with the tree variant.
Lush caves and all new plant related items in them: All non-canon items will not be added, and lush caves should spawn close to the surface in jungles.
Deepslate: Should not be added.
Powder snow: Should spawn in patch's in Misty Mountains and Forodwaith.
Axolotl: Technically canon, should spawn in caves in warm biomes.
Goat: Should spawn in mountain ranges.
New cave generation: Rather complicated, probably won't be added, although it may have to be.
All of this should be up to the mod team. I am interested to see if they can implement the various new stone variants in a canon way.