You are right about the reduction in overnight service in Europe. It was a combination of actual market changes caused by expansion of the high-speed networks and the Gardner Doctrine, that the advent of discount airlines and chopping up of the system into corridors made overnight service obsolete. In the lull, Flixbus and other long-distance bus companies were handed the market, with a few exceptions.A 4 person couchette is pretty nice even if there are just two of you. One person per couchette would be luxe! I took the Trans-Siberian from Beijing to Moscow twice and both times once we got past Ulaan Baatar there were just two of us in the regular 4 person couchette. Not great, but fairly good. The only problem was the horrendous condition of the toilets. If I could have had a couchette to myself with no extra fee I would have been a happy camper.
Hearing about about overnight trains in Europe is good news. It seems like a lot of the longer distance sleeper trains went away for a few years, or so my searches seemed to indicate. I think I took a single IC from Berlin to London (though in retrospect I think I may have switched trains in Brussels) back in the day. But it really seems like it was a single train all the way to London. I think most of the longer rail trips in Europe are now 2 or 3 segments. Or so my searches on The Man in Seat 61 seem to indicate. Great site for planning international rail travel.
How to travel by train or ferry from the UK into Europe & worldwide... Train times, fares, how to buy tickets, advice & information.www.seat61.com
In the absence of overnight trains, as I've written before, tourists and rail-oriented business travelers were hit with bizarre itineraries by the trip planning software. Some people saw that a niche market remained and that combined with "going green" is leading to a revival. The DB - which did in its own CIty NightLine - has introduced some ICE trains that are in effect "owl" routes, such as Berlin to Munich overnight via Frankfurt. These compete with the bus lines. In the meantime NightJet has expanded and has some interesting links such as with SNCF for Paris <> Berlin overnight via Strasbourg.