Not sure what the best way to deal with this is, but a forced downgrade definitely isn't it. It's ultimately about ordering who would be IDB'd, and taking care of them on an alternative flight in the cabin they purchased. I can tell you this, I've never flown in Y on longhaul ever in my life and wouldn't do it period. Certainly not for $800. The notion that both the front and back of the plane gets you there is ludicrous and is undermined by all that DL does to "protect" the front of the plane on longhaul flights.

I don't really care what DLs contract of carriage says, I can't show up on day of departure and make radical changes to my ticket without incurring significant penalty. $800 for them to downgrade lacks any symmetry. Sure you can cancel and go home, but that's entirely unfair for someone who buys a ticket in the business class cabin because that is where they fly. There are damages here that far exceed $800 and DL's attempt to cap them at that is unfair!

I've only had to do this for my wife before when they tried to stick her in coach for 24 hours on a confirmed business class ticket, but I made the airline (former NW) find her a proper business class routing and pay for her hotel and involuntary stopover costs.

Shame on DL for doing this, even if to only 3 or 4 passengers (that we know of) so far.