Great blog post! I think this is something more projects (within and outside of Mozilla) should give more thought on.
In general I think it’s good to have “Open Tasks” and specifically keep an eye out that you have some of them around. In a project like Mozilla though, it should be the default though, and just tasks which really can’t be done by a volunteer, should be something else. But that’s just my opinion. 
Another thing is, maybe not directly related to “writing” a good, open task, that in bigger projects there are always tasks lying around that nobody has been checking for a long time, either for comments like “can I work on this” or even if they still need to be fixed or not. Within Mozilla this is mostly a problem within Firefox OS components. Is there any project to make this better?