I think claims about HS2 killing the CS are a forum thing based on conceptual theory rather than considering the broader realities and users of the service.Therein lies an advantage of a sleeper train. For those in the land of nod between midnight and 6.30am, the train journey effectively takes about half an hour on the Lowlander. I know people claim HS2 will kill off demand for the Caledonian Sleeper but it seems booked solid most nights at present and of course cheap flights may not be around forever. Given the apparent challenges with lack of rail capacity between Glasgow and London to absorb those who presently fly, perhaps there's justification for running multiple sleeper trains to/from Scotland rather than only the two journeys we have today.
I also agree that there seems to be the demand for more sleeper services as well.