In reguards to the topic of the original post, i think that it's a good decision to make, although feel it should've been sooner, especially given the safety risks of no door locking and the bad press of toilets dumping on the tracks.
I'd question why the current extemption is to March 2023, rather than to more coencide with the rules applied to normal passenger stock on accessability, maybe to have had central door locking and retention tanks required by the end of 2020 (assuming that "you know what" never happened).
In the years to come i can see there being a requirement to put locks at droplights in a similar manner to how it currently works on the Night Riviera sleeper to reduce the risk further, maybe allowing the window down a little bit more than on the sleeper but no more than a couple of inches. With hopper windows in the carriage buffers to be fitted inside so the window can be open, but again no where near wide enough for a head to poke out of.