Many of the northern European countries have withdrawn sleepers as passengers seem to prefer a high speed trip and where necessary a stay in a hotel. I personally prefer to do that these days, get a nice meal, a beer, sleep in a static bed, shower and perhaps an early train.
Peoples ideas about how/if they travel will change upon the easing of C19 measures.
Idea is good but I'm failing to see any way that it could make any money.