i like this. i think for now as a workaround: one could lock the topic and leave a comment asking the OP to crosspost it elsewhere, with grace for posts which have high engagement (as ladfrombrad suggested).

i don’t agree that crossposting works to ‘move’ posts. as far as i know: the OP is not notified when their topic is crossposted by someone else, and in that case they also won’t be ‘subscribed’ to comment notifications.