I have a similar use case, but a different solution: The ability to create a followup link to a particular message (optionally: an entire conversation, or label).
I'd want to push a button on a message (or on the thread) labelled "follow up" and get a new message that I can edit, that contains a link in it to wherever I was. This is an operation like reply or forward, except it's always to me (and additionally, perhaps, Cc'd to someone else)
Followup messages go into a special "Follow Up" folder. The annotation can be edited and amended as needed. If I Cc it to someone else, I'd like it if they could edit that followup annotation with me, perhaps using Google Docs,
Ideally, I would be able to enter a date/time for a reminder and have that added to by Google calendar.