A promotion like this will attract throngs of frequent flyers on the east coast. It's a reasonable guess that frequent flyers will want to travel at peak times between popular city pairs. If bookings are not available the "unlimited monthly bookings for $599" will lose it's appeal as there are only "x" number of seats in the market. The alternative is to heavily overbook the flights, that's what I meant by standby hell (Booked to 120% LF and everyone shows up!)

It's great marketing and should do wonderful things for Load Factors, just book all of your seats early!