The idea of using airline first class 'pods' makes perfect sense. You could instantly increase the capacity of the sleepers to make them far more financially viable.
Every person boarding could be given a small bag (like most airlines give out) with ear plugs, throwaway toothbrush etc and the toilets could be vastly improved with more of them. I guess facilities at the terminal stations might need to be boosted too, given you could have a lot more passengers.
First class could continue to offer actual compartments with en-suite facilities added.
Sleepers make perfect sense, but they're not advertised very well - and no doubt because there's not the capacity. So TOCs have the choice; invest and make it a lot more successful, or run it into the ground and axe it. The latter is easier, obviously.
I hate stupid early morning wake-ups to fly somewhere, and going the night before with a hotel stay isn't much better as you probably check in really late and it messes up your body clock. Getting on a train where you can turn in straight away, and the cost is probably less than a hotel, seems very logical. Going forward, I'd expect sleepers to be introduced on services through the tunnel as you could then begin to travel to far flung parts of Europe without changing train, and not losing most of the day in travel.
But, I think I may be dreaming!