I was talking with Meower earlier, and we both thought it would be very interesting to have a compilation mod of other people's (rejected) ideas, inspired by INSmod.
If you guys send me your individual .gmks of whatever classes you want, I can compile them into a fan mod. This means that you have to sprite, code, and implement your ideas yourself. Of course, during compilation, the class will be subject to some balancing/improving under my discretion.
If it turns out some of the ideas are good, I might use it in the official build. At the very least, this forces you guys to make your own content (for an open source game!), instead of coming up with ideas for me to do (which will never happen unless you put some actual work into it).
Edit: tl;dr if you guys put the work in, there's a 200% larger chance that I'll implement it.