(for my few long hauls I don't care, as I always book the cabin I want to fly - so opups are just physically not possible from that class).
But when the originally booked eco is oversold - it means: Seat blocking will not work.
And will a FTL in Q really be opuped, while a HON in V has to remain cramped in eco (just 'cause he paid 40€ less?) ?