Seen fairly aggressive seat blocking of the mini cabin on the 4 class 77Ws for a few months now.
On a multi-pax booking (self-DM+GO/SL/SL), I’m only able to assign a seat in 11/12 for myself online. No problem to get for the others when calling in.

Not a clue as to how it would work on split reservations/status-less bookings.