You already know about this idea, but I figured I'd "transfer" it to the issue tracker so you can update it as finished, not going to happen, etc.

An NBT data for the metamorphosis like {Life:200s}, where the "Life" determines the time before hatching in ticks, would be cool for custom spawning mechanics - you could have a "vespa nest" with dormant cocoons, and so on. With this in place, maybe you could offer an additional config option for how long it takes a cocoon to hatch into a vespa.

Should already been fixed in the current version