>Instead of moving the thread to the other forum after just one day, move it after at least 2 BUSINESS days and have a flag at the top of the messages indicating that this thread will be moved in x time to the y forum, where it really belongs.
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>That way if 3 years from now I need to look something up I know it's all nicely archived in the appropriate forum.

Having a flag like this would be a notice of an upcoming thread move but I don't see how it would help you if you do a search in three years.

Having such an implementation requires an additional lookup when viewing each message, a pending table, plus ongoing checkups by a robot. I'm not sure we want to implement such an ability just for that. Like I said, rarely such a feedback is provided. That will also encourage people to post in a not most appropriate forum.