An improvement I am going to suggest to GWR▸ is that they know who have booked affected trains, so why not email them & let them know? Quite easily done, I would have thought.
Not impossible, but would need cross industry co-operation to be completely effective as not everyone books a ticket for a GWR train on the GWR website. Also if someone has booked via say the Virgin website and has ticked the opt-out box could the address even be passed on under data protection laws?