Road travel is very rarely smoother than air travel though. I've actually been to Singapore on BA's lie flat beds, as well as bus seats that weren't far off in basic comfort, and train beds which were much more comfortable and generally smoother than both yet remain a very niche form of budget transport. Taking an order of magnitude longer than air travel means the overland options are still rarely a better fit (the sort of road trip that can be done overnight without interfering with schedules is also a nice short evening flight, and I'm happier emailing on the plane too).
I can see the appeal to some demographics for some itineraries, but can't see people preferring a series of road trips amounting to 40hrs over a 4hr flight being a mainstream market.
I've taken sleeper train services before from Scotland to London. It's cheaper than a hotel and the service leaves at 11pm and arrives at 7am. You get a room with a real bed (and lockable door, sink, toilet, etc.) and a pretty decent restaurant and bar to avail yourself of. You also get to leave from the city center and arrive in the city center, without messing around with security and arriving 1-2 hours before the flight.
