Weren't there reports of AA doing this about a year ago? As a frequent traveler I agree that I have no incentive to board early with only a small item that can fit under the seat. I rarely even board with F in that case. However, the airlines have conditioned travelers, particularly infrequent travelers, to view early boarding as a perk which would make this a win-win; the passengers get the early boarding they desire and the airline gets a more efficient boarding. BTW, I fly WN occasionally and have never heard this announced at the gate.