Didn't something like this used to be done on the mid-morning weekday service from Inverness to Kyle of Lochalsh in the 1980's?
It seems utterly bizarre to me that the West Highland Line doesn't have it, for one.
In the 60s Observation cars ran:
Inverness to Kyle
Glasgow to Oban (via Stirling - and I'm pretty sure continued via Garelochhead when the old Caley route closed).
Glasgow to Fort Williiam
Fort William to Mallaig
With turntables at all termini they were turned and always on the rear of the train with the receding view through the end windows.
The first two were ex Devon Belle cars - one still running to Kingswear, to fort William and Mallaig they were the ex LNER cars with ends rebuilt to provide a better view (I think both are preserved - I travelled in one on John Cameron's Lochty Private Railway behind Union of South Africa (propelled on the return trip)).
Early 80s BR tried again using ex LMS and LNER inspection saloons Fort William to Mallaig, and an ex DMU driving car to Kyle.
Like everything today cost of provision would be the issue.
The Swiss have long recognised people will pay a premium for a better view in more comfort, in the UK a Business Case would be required with the those against reluctant to take a punt on what, taking the long term view, might well prove to be a commercial success. Over to you Transport Scotland - with pressure from local Tourist Boards!
EDIT: Or maybe a Grant Aided project for West Coast Railways to do a complete rebuild on a couple of coaches for use on the Jacobite, probably less seats but revenue protected by a premium fare.