I feel like I or maybe some others need to write about pony fusion. Just imagine the extra thickness of Princess Celestia and Princess Luna combining into each other? And others? Like all the princesses or something? The entire mane six etc. Human lover will have extra thick mare to love.

A perfect example. Under safe tag on derpibooru (so free for me to share): https://derpibooru.org/images/2596770?q=fusion

Look how thick she becomes with the two of them combined? Holy moly.