Some food for thought:
- you can already mark (flag) posts as off-topic. If mods would agree to split off a topic that was marked as such by sufficent people: problem solved
- reputable forumers have the power to rename & move topics (cool),
but not to merge (5th person opening a topic bc they need WhatsApp or a refund) / split a topic (uncool) - the forum is more powerful than people realize: after clicking reply to somebody, you can choose to do so in a new, linked thread (arrow symbol top left)
The incident that broght this up was a bit unfortunate. IMO, there was a harmless, playful, tounge-in-cheek, mildly off-topic “but my gaming platform is better than yours” exchange that quickly became more off-topic and more serious (almost another Win vs Linux war 
)
It was almost like somebody would throw “2D is better” in the room and then somebody would seriously debate it. (Sorry, @2disbetter i had to 
)
The original first off-topic remark was not off-topic enough to justify a new thread. Only in hindsight is it the post where it should be split off.
A complicating factor in splitting topics is that you can either only do it if all following posts are (still) off-topic - or (if the software allows it) you are willing to spend some time separating them.