The ability to export OTG biome settings (primarily colours) to a datapack so pre-generated OTG worlds can be used without OTG installed if desired.

Don't think we'll ever be able to use OTG worlds without OTG and use a datapack instead, due to the way things are registered to mc / the world and initialised. For each world, we register a custom world type, a custom noise generator, custom biomes etc, all using the OTG namespace. The odds of any of that working without OTG installed, and a datapack to substitute it, I think are very small.