Is your feature request related to a problem?

There isn't a way to set biomes to be per-player

Describe the solution you'd like.

In the PlayerChunkLoadEvent or a new superevent of that, there should be a way to change the biome data sent to the client in order for each player to be able to get a different set of biomes.

I think this has to be a new superevent of PlayerChunkLoadEvent because biomes can change independent of chunks being sent to the client with the new fillbiome command. There is also a specific packet for changing a chunk biomes.

Describe alternatives you've considered.

N/A

Other

I'm not sure of the correct API structure for representing chunk biomes. Generally, I think it would be beneficial if plugins could create chunk biome data arbitrarily to they aren't creating new PalettedContainers for every player. Having some way plugins could create biome data, cache it, and then use it for specific players would be ideal.

ChunkSnapshot is a good place to start. It wraps around 2 arrays of PalettedContainers for blockstates and biomes. Having a supertype of that which just wraps biomes seems like a good idea.

Something to note is that the array of PalettedContainer for biomes has a different length depending on the height of the world. So care would have to be taken to ensure that the sizes matched.