I'm not a user of either, but I've heard quite a few people hit a limit where Vue no longer worked for them and they needed to refactor their code to another system, but I haven't heard of anybody 'outgrowing' React.
I think sometimes people over-engineer with React, but I don't see problems where people simply hit a wall and can't go any further without ditching their tool first like I've seen with Vue.
I do wonder though, if Vue-like things like weex.apache.org can help the Vue side of things.
I think there's plenty of room for both to co-exist, and from this point in history will be hard to predict which will be in use longer.