One thing that hasn't been mentioned in respect of Advance tickets will be the need to make sure 'through Advance' tickets are properly offered. It's no use LNER, Avanti, GWR etc offering copious numbers of cheap Advance fares on theor own trains (I doubt they will anyway but we can hope!) only to then have to purchase a separate ticket for a connecting train.
This could be another hidden price increase via the back door.
This could be another hidden price increase via the back door.