There is currently one first class seat remaining on the 3:25 pm flight from MIA to JFK this Sunday 9/17, which Delta is offering for sale at $1500. I don’t see this as any more or less “classy” than offering it to the highest bidder at the gate if it remains unsold, as opposed to giving it away for free to some lucky customer. It doesn’t literally have to be an eBay style auction, of course, they could also send upgrade offers to passengers’ phones at steadily decreasing prices until someone accepts.