we're gearing up to 4.0.0-beta1 this month. Which will be the cut-off point for any API changes in the 4.x release line.
Any API changes after this month won't be in a stable release until 5.x (mid 2018 according to our roadmap
So if you want to get (smaller) API changes in, raise a pull request in the next two weeks - allow some time for peer review and discussion.
Here's a handy list of all issues in core repositories with the label "change/major".