Anything that saves lives/prevents accidents must be a good idea, and
deserves investigation.

Monitoring trains is done to a very limited extent to evaluate ride
quality - once every 2 months, I think - using portable equipment that
is removed from the train after each journey. Which is a start.
A couple of trains on each line could be instrumented permanently,
this would give some sort of control over ride quality, and reduce the
risk of derailment caused by track condition. Monitoring every train
might be too expensive at this stage, but will probably become viable
with future improvements in technology.

I'll see what I can find on derailment info and get back to you.

John