For reference, I'm talking about this, and I don't just mean edge biomes, mutations and oceans. Despite including the following code:

#Remove other biomes all = forAllBiomes() all.set("genWeight", 11) all.set("isSpawnBiome", false)

Biomes other than desert, river and ocean end up spawning. Just flying around in creative mode, I've also found jungle and plains biomes appearing so far.