Provide direct feedback for rejected migrations
Closely related to gnat's recent suggestion which I agree with in spirit -
If a migration to a SE site turns out to be a bad one because it gets closed as NaRQ, Off-Topic, or too localized, why not automatically inform the users who caused the migration using a notification bar as you get with new badges and such?
It could read
Question x that you voted to migrate to X.SE was closed there as "Not a Real Question". Migrating it there may not have been the right choice. If you're unsure, learn more about how to do a good migration here. (link to a good canonical Meta resource)
this would reach exactly the right people - those who botched the migration - with zero human effort. There wouldn't be any kind of punishment; just this message. I think this could be incredibly educational.
As to how long after migration a closing would have to happen for this message to be shown, I don't have a perfect answer to that but I'm sure it could be determined. One would want to err on the side of caution - i.e. if in doubt, don't show it. The right recipe would probably be some formula of the number of views vs. time. Alternatively, a fixed per-site time limit (e.g. a day on SO, 3 days on less frequented sites) might work. There would also be exceptions: If a migrated question gets closed by a mod within a day of migration, the message would be triggered; if it takes, like, 300 views to get closed, it would not.