I booked the DCA-LAX nonstop on a Saturday evening in November, and put in for an RUC upgrade. There are still 13 D1 seats (out of 16) showing up as available on the seatmap; I was waitlisted. You could buy a seat today, 30+ days out, in D1 for $588.00. Hopefully I'll clear prior to the day of departure, but who knows.
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I was lucky with my first group of 4 RUCs. I actually went 4 for 5, missing out on F on a JFK-SEA trip. I was able to use my 4 certificates for flat bed travel (the inaugural DCA-LAX being the highlight, but also on an ATL-SFO 767 positioning flight where I used my RUC 3 hours out to jump over 7 flyers and into one of the last two UG seats, and a SAN-ATL 767 where I got the last UG seat, 10A).