Unknownreported this suggestion
Summary RandomSpawns conditions already supports a CUSTOM option from Bukkit. Beyond that, there is no way to enter a value for CUSTOM to set the condition.
Usage
Something like Biomes: CUSTOM Namespace_My_Biome_Name (would probably require the namespace)
Value
Having this option added would allow developers running custom world also generating custom biomes to use the BIOMES option in RandomSpawns.
Priority
Not sure, I've seen two other requests for this in 30days. Probably low at this point, but as datapack usage increases (and it has been) this is going to become a bigger issue.
Implementation
Uncertain, out of my scope of technical expertise, which is pretty low. Sorry.