DOO / DCO is part of Northern's franchise agreement. Arriva don't have a choice and seems to be heading towards a DCO Scotrail type deal. If it was their choice I think they wouldn't implement it.
It is but my understanding is that the agreement has plenty of wiggle room on the subject and is, of course, a proper franchise rather than a management contract like GTR (so the DfT can't meddle to quite the same degree without Northern saying 'okay but we're going to reduce our premium by £xm' or 'okay but we're going to need £xm more in subsidy' or even 'no we're quite happy with the agreement thank you very much'!).
So, for instance, the franchise agreement would appear to be satisfied if Northern introduced DCO with ten bell dispatch by a safety critical guard. This is the same way that Voyagers work for example. The driver is in complete control of the doors but will only close them on instruction from a guard and will only set off when given RA by a guard (though I suppose you could use CD/RA where dispatchers are provided).
If I were the RMT/ASLEF and Northern came to me offering that along with a guarantee that it would last at least the length of the franchise (currently due to end March 2025) I'd struggle to turn it down I think.
Nonetheless, it is only right that they properly discuss the T&Cs of such an implementation, as well as pay closer to the time when more details / timescales / impact on crew roles is better understood by all. As I read it, this is what Northern staff are most concerned about.
I wonder if a two year deal with an optional third (i.e. either party can walk away after two and go back to the table otherwise a third year on the same deal) might not be something a compromise that could work? Also worth remembering that we're already most of the way through the first year of the deal as we're negotiating the pay increase from April 2016!