I have found that when creating a new world in Minecraft Realms, the LargeBiomes generation option doesn't work. I selected LargeBiomes before creating the world, but the world I came into was default generation. The reason I know this is because I played on the same seed in a single player world with LargeBiomes, and the spawn looked completely different. I also looked up the seed on Chunkbase.com and found that the world is indeed a default one.

Steps to reproduce:
1. Create a new world in single player, with a seed and default world type
2. Create a new world in single-player, with the same seed and Large Biomes
3. Create a new world in Realms, with the same seed and Large Biomes
4. Watch how the Realms world is identical to the default world and not the LargeBiomes world