99% of Passengers could not give a hoot about variety, they are only interested in getting from A to B without the train being cancelled and on a clean comfortable modern train. None of the previous GA stock (and I include the 170's , even they look tired) really meet that criteria, the sooner all the 15x stock has gone the better.
A fair proportion btw might be upset that the bi modes use diesel, Internal Combustion Engines have the future of the Dodo and we need a carbon free Transport Network asap. I am sure the 755s have much lower NOX, PM and CO2 emissions than the trains they replace, but the sooner they can replace the diesel power plant with batteries and some form of charging when at terminii the better. perhaps the imminent advent of high density solid state batteries will mean the diesel power plants are a stop gap.
The 170s are a pleasant train to travel on once you've worked out where to sit to avoid the worst of the engine noise and vibration.
I can see that in the future it would be relatively easy to replace the 755 power unit with "something else" - be that batteries, hydrogen fuel cells, CNG engine etc. If the "something else" needs more room you just build a slightly longer power unit.
Agree that most punters (me included even as a rail enthusiast) want a clean train, on time and with sufficient seats and catering.on the intercity route.