I think the seat poaching issue is about customers moving into EMPTY, unassigned premium economy seats without paying....not sitting in a seat assigned and paid for by someone else. The interesting thing about it is that on elite-lite flights, where all the elites were upgraded but nobody in Y wanted to pay for premium economy, you'll have two situations....those without Y seat assignments get premium economy for free if Y- is full or you'll have this weird situation where the back if packed and the front rows are empty.