I think it may sound weird... However, I would like to spit out an idea on Gmail Inbox...
How about having personalized comments in the inbox?
This would be similar to draft message but for personal use.
For example when you see an Email, your first response might be different than the final response draft you are looking before the Email is sent. Drafts are handy because it allows re-iterations. But they are gone once Email is sent out. All the secondary thoughts are vaporized at the moment the send button is hit.
Having comment enabled on Inbox Emails will allow more personal approach to the Emails. Just think of how handy the comment features are in the spreadsheet: (generally) are not printed, but are useful.
So, Gmail Team: How about having "comment" feature available in Inbox?