I'd like to suggest config options for custom ores that whitelist or blacklist ores from generating in specific biome ids or categories, like so:

[["Custom Ore"]]
	"Ore Name" = "minecraft:emerald_ore"
	"Filler Name" = "minecraft:stone"
	"Max Vein Size" = 1
	"Min Vein Level" = 1
	"Max Vein Level" = 256
	"Spawn Rate" = 2
	"Biome Category Whitelist" = ["MOUNTAIN"]
	"Biome ID Whitelist" = ["minecraft:mountains", "biomesoplenty:alps"]

This example would limit emerald generation to a few mountainous biomes. For the example, I mixed using categories and biome IDs, but that probably wouldn't be very helpful in an actual config.

A whitelist that overrides an optional blacklist would be neat.