If Windemere was in Switzerland it would have been done in the 70s as part of the WCML. As well as the HGVs being moved by trains.
Certainly the German-speaking countries seem to be particularly keen on electrifying relatively minor lines. A case in point, kind-of related to Windermere in the sense of being in a mountainous tourist area: not only is the secondary Munich-Garmisch-Innsbruck route electrified (an equivalent line in the UK probably wouldn't be) but also the branch at Garmisch through Ehrwald to Reutte in Tirol and even the small branch to Oberammergau.