Whilst it is available to passengers between Fort William and Edinburgh, the train is classed as Reservations Compulsory and therefore may not stop at request stops without a booking. In particular Glasgow Queen Street often gets skipped northbound if running late.You can certainly do it - you'll see people getting on and off the seated carriage at intermediate stops in both directions - but the impression has been for a long time that CS only do it reluctantly and really would prefer to get shot of the duty.
It's rather disappointing to see it removed from the Scotrail timetable, giving potential users of the WHL the impression that there are fewer services than actually are available to them.
It does still seem to come up in online journey planners though.
A friend of mine used it for hillwalking a couple of years ago, got an ear bashing from the TM for not having a reservation who also wouldn’t sell a ticket.