Whilst I often see the guard checking tickets on the Harrogate line, quite often the doors can delayed from being released at a station for up to 45 seconds whilst the guard has to walk from the front car to the rear vestibule to release the doors. And then there are of course the services which the guard makes no visible presence in the saloons at all, because the stops are so frequent.
Whilst I do think that there are some excellent Guards in the industry who really are a testament to Northern and other TOC's, can you really blame Northern (or the Dft) for trying to change something that is currently inconsistent into a more consistent package that will retain a second member of staff who will be more customer focused and will generate more income for the company by uninterrupted revenue collection.
Even if some routes was to go DCO, I would not imagine that any trains would run without a second member of stuff given the nature of the network and the amount of lost revenue that would incur.
If northern was not able to press this far, at the very least I could see a scot rail approach being used (driver release, guard closing) to minimise the delays in releasing the doors.