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China's approach seems to be one of the best: bullet train soft sleeper, capsule-like design, individual windows.

https://youtu.be/DAOYz8FcDiQ

Japan has also nice sleepers, but they are not bullet trains, plus, way way more expensive, and not a mass phenomenon.

[lmm]

There's one (and a half) last scheduled sleeper train in Japan (as distinct from luxury cruise trains), the Sunrise Izumo / Sunrise Seto, which has fairly reasonable prices, although as you say it's a conventional train and much slower than the Shinkansen.

[eynsham]

The trains you link to only go at 150km/h to minimise noise, so using ⩾300km/h-capable rolling stock might be a bit of a waste.