This (or a form of it) is, in fact, the current top thing on my TODO list.
The main solution I'm going with is basically your #5: I'm building support into the game for honest-to-goodness "message attachments," and when you send a message, you'll be able to see a list of your scout reports that you can attach to the message just by ticking the checkboxes next to them. The whole immersion-breaking ID/Hash thing will disappear entirely; you'll never have to see that again.
This should also open the door for some other interesting innovations in the future, but I'm going to try not to get ahead of myself too much.
