would have also been interesting to see an electric powered train try to get down to Penzance without wires!

Don't see why not ... an electric powered train made it to Minehead the weekend before last. The Hastings diesels - as I understand it - have electric traction motors which are powered by onboard diesel generators.
Electric traction everywhere in the west.
HSTs▸ , Vomiters, Class 66s, Class 57/3s....