The more you delay the upgrade, the more painful it becomes in the future.
At a previous workplace we had to go from React 0.13 to React 15. We had to re-write, fork and patch, or get rid of entire third-party libraries. There are no stepping stones in the JS ecosystem that let you do gradual updates if you are several versions behind.
It's very easy to upgrade React incrementally. The only problem is that it's likely not so easy to upgrade your related dependencies incrementally. Especially if they use internal APIs or aren't regularly updated.
There are in the Ember community. They do such a fantastic job of transitioning between versions.
I have had my complaints in the past when I don't touch an Ember app for a year, but for the most part, they provide ample "stepping stones" to bring the community along without too much anxiety.
At a previous workplace we had to go from React 0.13 to React 15. We had to re-write, fork and patch, or get rid of entire third-party libraries. There are no stepping stones in the JS ecosystem that let you do gradual updates if you are several versions behind.