I really love this plugin idea and I want to use it in place of the various calendar programs I've tried when managing my blog(s).
The one thing that keeps me from using this is that I really need an editorial/tasks calendar in one. For my blog I often need to accomplish certain tasks before a post can be published. So sometimes I would need to attach tasks to posts.
As an example, I run a book blog and often interview authors. So an example of this situation would be:
1. Contact so-and-so author to schedule interview date.
2. Email so-and-so author with interview questions.
3. Write/Schedule post.
That's just a simple example, but one I need so often. I need to not only be able to see my upcoming posts to make sure I've got all my ducks in a row, but also the upcoming tasks I need to do in order to make those posts possible. I haven't yet found a plugin to do this.
Hopefully this is something that can be considered within the scope.