This update changes the Nectere's biome source. Currently any existing world will be unable to take advantage of the new biome source type because a world's biome sources are locked in in its level.dat file. This means that currently, in order to use the new biome source, you would need to manually edit your world's level.dat file. This is a pretty messy requirement and not trivial for most users.

Heart of the Machine should automatically change the biome source for existing worlds if a config option is enabled. This config option should be enabled by default.

Oh new versions, this is handled by QSL.