I had a bit of an idea for how the future of SK could be formed.
What if SK enabled the Steam Workshop? Users could generate levels using the preset assets in the game, or if you really wanna go all out, have them be able to put custom models for weapons and items in the game.
Sound good? No? Discuss your opinion.
Best way to support custom content is not to do so through Steam since a large number of players play from other places (Kongregate, official launcher). This would essentially cut out the ability to contribute to the game.
Instead I would recommend releasing some public tools. In-game tools can consist of a level editor or hue shifter (for reskins). Out of game tools can consist of model and texture documentation and a public place to submit items. Additionally some "code package" to have the items prepared for releasing.
Have all community content be publicly viewable on github or something. People can "fix" items introduced in this way, submit their fixes, and potentially get better items.
So yeah, community content good. Limiting all community content to steam workshop bad.