Split two 153s? Last time I checked Church Fenton wasn’t permissive and even if it was, what a ludicrous idea.
If this all hinges on the Hull <> York going via the main line (vastly quicker by coach I suspect if done properly), Sheffield <> York being so low in frequency that you can run Castleford <> York only every two hours (that sort of frequency doesn’t make modal share), and then people going Sherburn <> Selby have to go by bus (admittedly South Milford to Selby could easily be half-hourly) then why are we not just offering a bus from Castleford to York? We don’t expect many people to use the service so a bus taking in Garforth and Tadcaster and perhaps extended at its southern end to Pontefract could be helpful.
The equally sensible alternative is to extend the Huddersfield - Wakefield - Castleford around to Pontefract Monkhill and up to York; giving Pontefract an hourly service to York and then the Dearne Valley just being peak hour.
You'll forgive me a bit of blue sky thinking, but if the Sherburn - Selby flow is that significant, then it seems worthwhile giving due consideration of how to save it.
That said, do we really think that a Sherburn - Selby flow is likely to be greater than Normanton/Castleford - York ? You suggest Cass - York should be a bus (even though that would presumably involve a change of mode for Normanton people), but perhaps we should be diverting the Sherburn - Selby flow, preferably to a secent South Milford service, rather than depriving the five towns.
TBH, this is the one good idea I've seen on the thread.
The rest seem to be along the lines of "this existing service is poorly used, so we might as well do something - anything - to try to make it viable - especially an idea to restore a regular service onto a bit of generally unused route through fairly empty countryside". I'm not convinced that the "Deighton and Mirfield to York" market is that big (in fact, are there even commercial bus services from *Castleford* to York these days?)
Two points, firstly:
1. The Huddersfield - Wakefield service only runs to Castleford because one unit can't reliably do the round trip from Huddersfield to Wakefield in an hour (a round trip that is less than twenty five miles, as the cross flies) - similarly it takes two DMUs to provide an hourly Huddersfield to Bradford service (again, under twenty five miles round trip as the crow flies). And we wonder why the Provincial network is so heavily subsidised
2. If Huddersfield - Wakefield had been closed by Dr Beeching we'd have people demanding it's re-opening, promises that it could sustain several trains per hour, stuff about "why does everything have to go via Leeds" etc. However, the reality is that the West Yorkshire routes that don't serve Leeds are pretty quiet affairs - planning a service from Huddersfield to York that avoids Leeds (and takes so long that it'll get overtaken by at least a couple of the four Huddersfield - York trains per hour) seems a waste of resources.
I'm not convinced that Wakefield needs a second York service per hour, but if Wakefield must have a second York service per hour (there's obviously already the XC services that take under forty five minutes, even with the long dwell at Leeds) then my preference would be:
That would give Knottingley/Pontefract a better commuter service into Leeds (which would be much more useful), it would give Barnsley a link to the ECML (bearing in mind that Barnsley is pretty badly connected, whilst Huddersfield/ Wakefield already have ECML services), it would have more routes that travelled in fairly straight lines (rather than the current nonsense of Sheffield - Castleford - Leeds and the curvet that a Huddersfield - Castleford - York service would have to take to avoid Leeds).
- Wait until Northern finally start their proposed Sheffield - Westgate - Leeds service (and hope that they find something better than a two coach 195!)
- Divert the Sheffield - Castleford service through to York each hour
- If 75mph paths along the ECML into York are restricted, you could limit the Castleford - York section to the hours when the Pontefract - York service isn't running through Sherburn (i.e. one path per hour at the York end, but alternating between "Sheffield via Castleford" and "Sheffield via Pontefract")
- Replace the Castleford - Leeds part of the ex-Sheffield service with a (second) Knottingley - Pontefract - Castleford - Leeds service
- Now that there's two reasonably fast Sheffield - Leeds services per hour (roughly forty five minutes journey time for thirty miles as the crow flies, so not mega fast), stop one of the Sheffield - Kirkgate - Leeds services at Darton and the other at Normanton once per hour
- As a speculative thing, you could then consider cutting the XC service at Leeds (there's already two TPE services per hour from Leeds to Newcastle, one of which will extend to Edinburgh, the Voyagers are in more need elsewhere, Birmingham to Newcastle is already faster via Doncaster, so use the freed up Voyagers elsewhere)
Not a major priority, in the grand scheme of things (when plenty of existing diesel services are crying out for additional capacity!), but more useful than some other suggestions.
I do think that Normanton needs two trains an hour to Leeds.
That said, other aspects of your idea could work, although there might be people from stations South of Barnsley who travel to Leeds who would be disadvantaged. As a regular on the Hallam stopper, there are reasonable numbers who stay on past Normanton, and I can't imagine they're all going to Darton.