Would really only just act as another way to set eggs as being able to be put into the Incubator instead of being tag-based. I guess maybe incubation time could also be set with a recipe json. Main reasoning behind this is to make a recipe book for the incubator be possible.

Even though this wouldn't allow datapackers to do anything with new incubatable entities, it may be possible to add an event into the mod for incubation completion which could be utilized by addon modders to do something upon incubation completion (like spawn an entity).