Is your feature request related to a problem? Please describe.
Currently with 1.16.2+ you can add new biomes to the worldgen folder of any given datapack. This works fantastically with Vanilla generation, but if you want to //setbiome afterwards, you cannot select the new custom biomes.

Describe the solution you'd like
Simply having an option to load custom biomes into the //setbiome list would be more than enough. If you need a set of biomes to test with Many More Biomes is a datapack with distinct biomes that I've confirmed to work on 1.16.3 for generation, however, do not load into WorldEdit Bukkit 7.2.0 Beta 5.

Describe alternatives you've considered
Making a custom tool to do so myself, however, that isn't exactly a good solution for the community at large.

Additional context
Using a Vanilla 1.16.3 client, no resource packs, running on Paper 204, I'm able to see changes to colours within biomes, however, WorldEdit Bukkit 7.2.0 Beta 5 does not load these with the //setbiome command in tab auto-complete, nor does it allow me to use them regardless. I've taken a look through the config as well to see if I could find anything there, but to no avail.

Custom Biome
Invalid for WorldEdit

the bukkit platform uses bukkit api for biomes, and the bukkit api doesn't support custom biomes, so this means either bypassing bukkit and using NMS directly, or waiting for spigot to add custom biome api support.