Do keep in mind that the depots have failed to do as requested many times over already. This plan also relies on a D stock being at Upminster on the evening of Thursday 20th and indeed that D stock being fit for passenger service.
I am planning to try to ride it, ideally on the journey which arrives at Upminster at 13:02, somewhere to the east of London.
Part of the issue for me will be avoiding the Oyster PAYG journey time limit - there was a time when I would have bought a 2-6 ODTC and not even thought of the cost but alas such no longer exist and the ride-at-will replacement is just too expensive.
btw, I travelled on the first train, on its first day, albeit not the first journey. So it would be fitting to travel on the last train too!