Excited about this idea. I wanted to do an overnight train in a Europe trip I did last year, but the timing and quality never quite worked out. A lot of the time, trains between cities in western Europe are annoyingly long for a day trip, but slightly _too short_ for overnight trips - almost like an NYC->London red-eye, where you arrive just after you fall asleep. The couple of overnight trains I saw that seemed like they'd work out timing-wise, like Paris to Venice, had really poor reviews, but I assume that's down to the various companies running these services, who probably haven't invested much in them lately as budget airlines continue to compete so heavily.

Sweden seems perfectly set up to invest in overnighters, though, as the article notes some theoretical routes. Norway and Denmark would benefit too, I think; at one point I was investigating doing a trip that would involve going from Oslo to Copenhagen, and the only reasonable non-flight options were an overnight _ferry_ (which, all things considered, was surprisingly cheap, though I'm sure they gouge you on food and the on-ship shopping mall), or a 7 and a half hour train trip that'd take all day. If Sweden were running overnight service along that route through Gothenburg, connecting those countries, it'd be a pretty awesome way to get between places.