There is a significant change in tourism world wide. It is not unusual to have significant numbers of tourists looking for different experiences from many parts of the world, and these will use the sleeper as a high interest experience. As Airbnb hosts in Inverness, in the last two years, I amazed that independent travellers with means are coming from all over the world, and from places we would not expect i.e. from south America, eastern Europe and the middle and far east. The season is also lengthening from February to October along with Christmas. Serco certainly will capture this tourist market.
However as has been said, the sleeper originally and still should be a strategic transport link with the North and London ( In the absence of UK length High Speed Trains as in Japan and China, which clearly remove the need for slow overnight transport.)
As has been discussed on another link here the Sleeper and overnight trains are GREENER than any flight. A strategic national intention would be to reduce carbon footprint and alter taxation, subsidy and pricing to reflect reduced emissions and maximise the use and modernisation of our rail network.