Invictus did a few "new" levels and made some boss monsters for the final waves. It's worth a look! http://psteamcommunity.yuanyoumao.com/profiles/76561198033496555/myworkshopfiles/?appid=201790

No, new maps are not supported. That's why you haven't seen any. Techinically it's possible because they give you access to the textures, mesh files, models, etc... It just isn't fully supported and would be a real pain in the butt as well as exremely time consuming, especially for one person. It should be pretty easy to change the apperance of a map but not the layout, in other words you can change colors and skins like with the character models. Tbh, I know a lot more about coding than working with visual mods.

I uploaded a mod that let's you have the Earth Lord, Fire Lord, and Fire Ogre on your team. You select and place them like traps then they act as they normally do except I made them guard a small area so they wouldn't be overpowered, only they fight for you instead of trying to kill you. lol I will continue to expand upon it whenever I get some free time, which isn't often. :/ That's not a new level but it brings something new to the game, much more than the simple skin mods and weapon mods I see people upload.

https://www.youtube.com/watch?v=H7-XEWKYvcM