As good as this sounds in concept, price wins at the end of the day, and while I lived in Europe RyanAir, SAS & Norwegian were a similar price to trains, but faster. The exception is when you travel to smaller regions with no major airport.
For the same price I actually prefer night train to airlines, by far.
Sure, airlines are faster, but the time to go in and out of the airport, security checks, boarding, etc... Your one hour flight easily translates into 3-4 uncomfortable hours.
With the train, it is usually downtown to downtown, just hop into the train and you are done. The journey may last 10 hours, but it is relaxing. Trains are much more comfortable than planes and sleeping is less of a problem, even with a standard seat.
With sleeping cars, you have what is essentially a moving hotel room, making your travel time effectively zero.
