I am going to make this suggestion while knowing there are going to be issues with it, however, I think it could greatly assist the games development and growth...
What I propose is a single player bare bones rendition of S4 League (A sandbox mode), to allow players to potentially offer complete creations to S4 League such as the capacity to create things skins, weapons, new skills, maps, etc... to offer as suggestions to add to the official game with the potential of allowing for prebuilt features that Aeria can then tweak (if needed) and ad to the game if it meets a set of standards.
The bare bones rendition would only need a "Map" consisting of a couple breakable objects to check damage values (of weapons) and very basic box shape in case of secondary features needed like wall jumping or skill testing. It would need some level of checking damage values with basic algorithms (They don't need to be 100% accurate given the test nature).
Given the fact they now have the source code, it should theoretically be possible to compile a basic version for people to play with.
While I am aware there are issues with stuff like piracy with this idea, however, I believe it could help the game grow and gain a more in depth community.