I'm gonna assume that what I read a while back about direct trains between Blackburn and Manchester Airport is untrue. It doesn't make sense anyway since changing at any of Bolton, Salford or Victoria would be much quicker.
Having read that Manchester to Rochdale is now 90mph and also that Northern plan to use 158s on the Clitheroe service, perhaps in theory this could indicate the Rochdale terminator will be from Clitheroe. It'd also make sense to include a direct link between Rochdale and Bolton in the Northern Hub plan, since Wigan (and the Atherton line) will already have one in the form of the Southport-Leeds service.
If my sums are right, Northern's franchise commitment is to operate 9 DMU services per hour into Victoria from the west, comprising 1tph from the Chord (Airport-Bradford Connect), 2tph from the Chat Moss (Chester-Leeds Connect and Liverpool-Leeds Connect), 4tph from the Atherton line (1tph Kirkby, 1tph Wigan Wallgate and 2tph Southport) and 2tph from the Bolton line (1tph Clitheroe via Blackburn, 1tph Blackburn). Of these, the three Connects and one of the Southport services must continue on the Calder Valley line through Hebden Bridge, the Connects to Bradford and the Southport presumably to Leeds via Brighouse. If the capacity of Vic to Rochdale is limited to 6tph per
lejog's Post #99, the remaining 2tph must be the Blackburn via Todmorden and the Rochdale terminator.
As you say, it would be advantageous to use 90mph DMUs on the Bolton and Rochdale lines, implying a Clitheroe-Rochdale service and a Blackburn-Blackburn circular.
This would leave the three remaining Atherton line services terminating at Victoria, assuming that the 319flexes will provide the 2tph between Stalybridge and Wigan North Western via Bolton, until the lines are electrified.