Just some Suggestions
Firstly I'll like to say that SpeedRunners is a Terrific Game. Its like no other competitive game out their.
Secondly, I don't know if these ideas have been already suggested, are being worked on right now or are to be worked on in the future.
Note: I have read the FAQ.
So here are my suggestions:
1. A short single player campaign for each character which may give some sort of back story.
2. If a custom map making program is released then obviously their should be a steam workshop. Player made maps which are "excellent" (depending on your idea of excellent) should be officially added into the game.
3. Cosmetic Effect Items? Basically alternatives to current items. So a missile could appear as a firework rocket instead and the explosion could be confetti instead.
4. More sophisticated maps. Basically maps where the pros can really stretch their skills to the limit.
Weather you use these ideas or not it doesn't really matter. Just keep making this game more awesome!