A persistent carry  has been enabling addition of the 'node-role.kubernetes.io/master' label to kubelet nodes. It would be preferable to find a fix that did not require a carry.
I don't know if we will remove this from 4.x. The number of modules it impacts is basically the entire system.
There is a PR to add both old and new labels , which might be a good first step to transition to the new label.
When we started on 4.0 this was a change that was added upstream. I do not believe we will be transitioning to the new label format and the carry patch will be required.