Meanwhile, back at the topic...
I can't see any benefit under the current arrangements for Northern to operate an EMU service north of Newcastle. Northern is primarily a DMU operator and, apart from this particular route, all of their services run out from under the wires. It may not be the most efficient use of their fleet to run a 75mph DMU under the wires to collect punters from places like Chathill and Morpeth, but it is the only realistic option they have. Providing an EMU service would mean either maintaining a tiny electric fleet at Heaton (probably just two units, one in service and one as a standby/maintenance spare) at some not inconsiderable cost, or pinching units from Neville Hill with associated long ECS moves. It wouldn't even assist in strengthening Northern's current diesel services, as I suspect that the requirement is for just one DMU which possibly works to other destinations away from the wires as part of the same diagram anyway.
Assuming no further electrification in the region, the best current option for an electric service would be for it to be operated by FScR using either Cl322, Cl334 or even Cl380 EMU's as an extension of the existing North Berwick service. FScR are an existing operator of EMU's and have both a sufficiently large fleet and are adequately provided with convenient servicing locations.
O L Leigh