This is moreso half an idea and half an issue where upon playing some custom worlds (most notably, the Aether), Elemental Creepers would pop up all over the place and just look out of place, not to mention making some dimensions extremely difficult.
I suggest allowing the player to have a configuration file where they can allow if Elemental Creepers can appear in specific custom dimensions and what type should be allowed to appear

(Also, an extra suggestion, perhaps have Air Creepers be a rare spawn mob for the Aether!)

Even just allowing players to set which biomes mobs spawn in would be helpful.