I think the forum is not the place for P2P trading, although no one is stopping you from trading via private messages, on forum, Telegram or anywhere else. There used to be P2P trading via slatepack market, but it is offline now: Slatepacks Market (relaunch)
Anyone can start a similar project, but the challenge is of-course guaranteeing that trade’s push through, dispute settlement etc. It can lead to a lot of drama. Therefore I do not think P2P trading should be facilitate on the Grin forum. Also I doubt it will attract many users. New users nearly always prefer the perceived “safety and convenience” of centralized exchanges.