I am aware that in emacs 26, there are plans to change the way in how certain packages can be moved out of the emacs master and still can be installed seamlessly using the tarballs of those.
At the time of releasing emacs 25.1, the org-mode in emacs master could have been synced up with the then 1.5 years newer and stable version of org (probably 8.3.5 or 8.3.6). But that got missed due to some reason.
As a precaution that that does not repeat when emacs 26.x is released, should the org version in emacs master be synced with the now latest stable org version 9.0.4?
If we are able the release the new packaging method in emacs 26.x, then we can remove org from emacs master completely, but if not, then at least as backup we have a newer org version to go out with that release.