The issue here is the desire of engineers across the world to use computers to control everything because they can not because they need to and the stupidity of the people running these companies be it Boeing, Bombardier or VivaRail to be seduced by technology.
SWR kept in simple with the class 455 conversion just change out the traction package and minimise the interface with other systems.
Sadly i suspect VivaRail will get no further in the UK now.
It's not about what engineers do or don't desire. It's usually driven by safety, reliability and economy requirements.
Technology usually ensures lower running costs and better reliability. If you look at cars for example the reason for many of the electronics is to minimise fuel consumption and manage the emissions systems. You can't do that with a mechanical carburettor. The last Ladas imported into the UK had carburettors and catalytic converters, the latter being required as a result of emissions legislation. The problem was carburettors were unreliable and inconsistent with the result that the catalytic convertors were damaged and the cars failed their first MOTs at 3 years old.
On the rails, many of the early AC electric locos had appalling reliability with not a computer in sight. But a mercury arc rectifier instead - effectively a mechanical solution.
