Interesting case of "back to the future" here with a new proposal for sleeper trains including routes between Europe and the UK (Night Star anyone?) starting in a couple of years: https://www.theguardian.com/travel/...-of-european-sleeper-overnight-trains-planned
(Starting it here rather than in Speculative Ideas since it's a confirmed proposal.)
(Starting it here rather than in Speculative Ideas since it's a confirmed proposal.)