Open source Pokemon, where new creatures can be contributed by anyone and anyone can add stories and adventures or fork the whole thing and do whatever they want.
The main reason for the commercial success of Pokemon is the huge array of readily available merchandise and anime/movie tie-ins. How would you go about replicating that with a crowd-sourced competitor? How would I be able to obtain a plushie for my favorite crowd-sourced character without paying the high prices associated with custom commissions?
It'd be open source so you'd get plushies, figurines, videos etc after someone else made them because permissive licensing let them use the art and ideas to do whatever they want. There would be nothing preventing a plushie company or a person or a DIY project making them affordable.
It would need to be curated, though, the way levels in Mario Maker are. Otherwise you'd just end up with people posting porn and ads or troll creatures designed to ruin everyone's fun.