A half-hourly EMU stopper between Huddersfield and Leeds is a given.
After that, it depends a lot on what you do with the Calder Valley. Personally I'd re-arrange the stopping pattern to get a half-hourly Chester/Manchester to Leeds via Bradford, running fast as far as Sowerby Bridge then calling at all stations. That would be supplemented by a half-hourly Huddersfield-Brighouse-Bradford-Leeds, giving a service every 15 mins from Halifax/Bradford towards Leeds.
The Calder Valley service via Dewsbury could continue as-is, providing a semi-fast link to Leeds from Brighouse/Sowerby and connecting some of the towns along the valley.
I'm not sure this will work. I think you have to presume that you've got 6 fast trains per hour from Manchester (either station), to Leeds, and then some towards York and some towards Hull.
I think I fundamentally agree with you about Northern taking command of the Chester - Warrington - Manchester corridor, albeit it would be at the expense of TfW. But, it would mean a single operator, and a standard service. And, running that up the Rochdale side via Halifax and Interchange to Leeds, that is entirely fair.
I don't think, if you want a half-hourly EMU from Huddersfield to Leeds, that you then have the capacity with 8tph running through Dewsbury to toss one in that's come from Rochdale or Blackburn, over Elland, and into Leeds via Dewsbury.
So I would personally say that if the Northern fleet replacement includes bi-mode unit options, get some of those. They would have equal benefit on stuff like Leeds to Carlisle (use wires to Skipton) and Leeds to Sheffield via Moorthorpe (use wires to whatever that last station is on the Donny route before you branch off), and a few others.
That way, you'd be able to provide a proper West Yorkshire Metro service.
- 2tph Chester / Warrington / Victoria / Rochdale - Halifax / Interchange / Leeds.
- 1tph Victoria / Rochdale (slow) - Brighouse - Dewsbury - Leeds (stopper from Mirfield to Leeds).
- 1tph Blackpool North / Preston / Burnley - Brighouse - Dewsbury - Leeds (stopper from Mirfield to Leeds).
- 1tph Additional stopper from Blackburn / Burnley (possibly Preston) - Halifax - Interchange and terminate, capacity buster / capacity maker.
- 2tph Huddersfield - Halifax - Interchange - Leeds stopper, possibly extending on to the likes of York or Selby as a stopper, so Bradford gets through service.
- 1tph Huddersfield - Mirfield - Kirkgate - Castleford - York - Scarborough.
- 1tph Huddersfield - Mirfield - Kirkgate - Monkhill - Doncaster.
That way you've got a three-way web of half-hourly services in and around Brighouse / Mirfield / Huddersfield. You've got a standard half-hourly service on lots of routes, and you've got better timetabling opportunities.