I dislike the idea of dropping Crewe as a passenger stop, the sleeper calls in were connections to & from the sleeper can still be made without overly long wait, Preston is a lot bleaker with longer waits for anyone needing a connecting train.
Theres zero passenger facilities at Birmingham Int that that time of night/morning.
We are talking about the Lowlander North calling there some time between 01:10 and 01:40 depending on what day of the week it is.
Highlander Northbound would be a bit more reasonable at around 22:50 - 23:10 depending.
Lowlander South you are looking at a 5am (ish) arrival at Birmingham Int which is already too late for check in for the early morning departures, add in delays to the service and your bang in trouble. Thats a pointless sleeper journey from Glasgow or Edinburgh anyway, Lucky if you're in the bed for 5 hours and even less sleep.
Highlander Southbound would arriving somewhere around 6am, by which time you've missed the early morning departures from Int airport. Again, any delays would screw you over.
Dropping Crewe is a bad idea in my honest opinion.