I've had this discussion in other threads; but, how wise it is to use these instead of vanilla JS in a project you want contributed to?

I personally find CoffeeScript very useful, and believe it's sufficiently widespread and mature as to be viable. All of these others though, I can only see it as increasing the learning curve on a project. I want to use IcedCoffeeScript (Oh, am I tired of Promises) and some of the JS extensions but I can't justify it. It's like a cake that I know I can't eat.