I guided my (small-ish) team away from VueX when we reached for VueJS earlier this year in an application. I based these decisions, at least in part, off of the GitLab engineering teams efforts, as well, for what it's worth. We are all still happy wth that decision. I don't have much more to add to the discussion but to say that it's very nice knowing that if we reached a certain level of complexity that we could, fairly easily, introduce VueX and be back at our previous pace without a lot of hubbub.