This is just a gimmick isn’t it, we’ve already got sensors under the seats that light up an icon on the dash if the seatbelt isn’t fastened when someone is sat in the seat.
That said I would find it helpful to have a led on the fastener as it’s a pain in the neck trying to locate the catch in the dark when you’ve moved the seat forward or backwards and the catch disappears somewhere down the side of the seat and the centre console.