Thanks for the prod on this one Christian. Another relatively easy improvement I really should get around to making.
I would also love this change! I use checkboxes a lot and find I have to manually update the cookies in headlines.
No update on this yet, however it is always good to see continued interest in a feature so thanks for adding to this forum topic.
When I took a look it appears more complex than I first thought - i.e. do I support just checkboxes, or also subheadings. For checkboxes you can have nested checkboxes, and ideally I should be updating the parent checkbox (and cookie) appropriately. When I looked at the behaviour in Emacs I can see that it isn't quite clear what should happen if you have both checkboxes and subheadlines - Emacs seems to try updating for both but the cookie total doesn't count both.
It might be that to start with maybe I forgot about support for headlines and concentrate just on checkboxes. Would you expect that checkbox hierarchies should update when all children are completed? (In an ideal world I guess the answer here is yes!)
Support for checkboxes only sounds like good start to me. Supporting hierarchies would definitely be nice, but not essential.