I don't know why I keep returning to this thread, maybe because I first travelled the line to Inverness with my father back in 1958. There have been a lot of changes since. Turning out some old junk during lock down I came across the picture below showing proof that in 1981 cars were still tagged to the rear of normal trains heading south. (I can identifty the Findhorn Viaduct at Tomatin in the second picture so suspect the other is fairly close by.)
One day I hope I can do the Edinburgh, Inverness, Aberdeen, Glasgow circuit exclusively by HST but it seems that can't be guaranteed for a few more months yet. Over 4 years since the project was originally planned.
I'm reminded of just how long because on 14th August 2018 a major motorway viaduct in Genoa collapsed without warning. There were no plans to replace it. Nevertheless a new bridge was planned, the remains of the collapsed structure together with neighbouring sections removed, and the new viaduct completed (during the COVID pandemic) so that within 2 years the link has been restored. I know, demolishing and rebuilding HSTs is different, but that was impressive work. The speed of this project isn't.