We don't think we'll ever have modding support for Ultimate Chicken Horse.
The reason is that the game was simply not coded with that in mind. Modding is not something you can just tack on to a game: it relies on the game using a programming architecture that allows mods to be created and integrated. It would also complicate crossplay between PC and consoles, since Steam workshop mods would not be compatible with console builds.
The only way to add modding to UCH would be to literally rewrite the whole game - and that's not something we want to do this far into development.