Most airlines already try to do that in Premium Economy. Typically it's the first 8 rows in Economy where there is more leg room and distance between you and th

Most airlines already try to do that in Premium Economy. Typically it's the first 8 rows in Economy where there is more leg room and distance between you and the person in front. The gate agents will try very hard to separate (block middle seats) for all the passengers in this zone unless it is an extremely full flight and not possible. Just upgrade (use points) to Premium Economy (do it at the gate once you know how full the flight is) for a fraction of what a middle seat would cost to keep empty. Good chance you might luck out.