More specific Biome ID groups to streamline Mob Spawn coding

In lieu of today's snapshot adding biome IDs specifically just for warm vs cold pig spawns, it's made me a bit more hopeful for this happening at some point. Something that could really cut down on a lot of maintenance work for adding mob spawns in the game would be to add biome tags that narrow down on different sub biome types. For example, while tags right now have general categories, if someone wants to have mobs only spawn in say a birch forest, there isn't a tag specifically for all types of birch forest, so they would have to manually exclude all other types of forests from the spawn parameters. Now, they could make their own Biome ID, which some do, but that could cause compatibility issues with mods and addons that add mob spawns and IDs for those biomes as well. More specific Biome groups in vanilla would help cut down on weeks worth of maintenance for projects that add in hundreds of mobs as well.