Thanks Mark - that was a very illuminating article.
One thing that surprised me was the comments about the noise problem with the diesel engines on the class 68s. I would have expected standards of noise suppression to have improved over the years. It also seems clear that class 68s will not be the apparently obvious solution to the traction future of the Night Riviera I assumed it might be. Would anyone be prepared to provide funds for a bespoke 6-axle solution? Sounds doubtful.
It surprised me too, & they've generated complaints elsewhere for being generally terrible neighbours. Also, yes, you'd expect things to have improved, especially given that it's a loco.
Which reminds me to take a photo of that 'Shut down engines' notice west of Bath Spa station if it's still there.
Mark