I’ve always found that it’s safest to roll Javascript. If someone wants to contribute and doesn’t like it (preferring CoffeeScript) then they can write it in Javascript and contribute the compiled changes.
If I put my PM hat on - it’s safe to say that in 5 years Javascript will still be here :). CoffeeScript will likely be replaced by … something. Or, it won’t look the way it does now and you’ll have language changes to contend with.
Javascript will likely always be Javascript. For me that makes it a simpler decision to stick with it.