@yonatanmn the reason I've been holding off adding a setState to stores is that it will dictate how immutability is done. some users prefer to use their own immutable library (immutablejs, mori, etc.), so with Reflux coming with their own means bloat for these users.
anyway - I think that opinionated setState (changeable or not) as an option is ok, and those who want to do it their own way should just alter state the way they want, ignoring setState, taking care of triggering themselves
(like react's setState which is opinionated by default...)