I have no idea if it's possible but if a topic is deemed to be off topic then can any further replies with that subject be forwarded automatically to another address like gentoo-dev-offtopic so they dont go to gentoo-dev?
I believe you can change the destination based on subject with an mta. the question is what does implementing this entail? and being that a subject might be re-used in a completely unrelated (to the original topic) or be put back on topic how do you decide when to remove the forward.