I recall China had comfortable sleeper buses back in the 1990s - when they had more gaps in their railway network. Tatami -style mats were enough, what's important is to lie flat. It can help sleep to feel a little movement, knowing you're going somewhere. But to succeed in europe they should integrate better with railway stations.

Yeah, those have been pretty common with similar comfort in Latin America since decades. I always wondered why they never made the jump accross the pond.

But traveling by bus kinda sucks. I rather take a sleeper train or a high speed one than a bumpy slow bus (or car).