Music too!!
Among us devs. Please. Make a page where people who may not be able to support you completely financially or just people that are pationate about the game can post their own skin designs, music, kill animations and trophies (trophies can be a MASSIVE rewards system where you pretty much will never run out of trophies to get BC ppl will be making them for you guys constantly).
i think allowing map design to the public would be a bit TOO far though.
Edit: also make people only able to post their ideas once a week and give them their skin for free if it is used.