Basically if the rumours are true about the EMR 156s going to northern next year means that there'll be only 2 TOCs that will have the 156s on the books, scotrail being the other one.
That's right, Northern will have 67 (or 71 if the Angel Trains units transfer back as well) of the 114 units built.
The Porterbrook units are scheduled to be released first, or at least in theory anyway. Hopefully they're refurbished to the same standard as the ex-ScotRail units.