You would really need an alternative service doing Stockport-Bolton. After the Bolton line is electrified the Alderley Edge turn backs would be the ideal choice but currently if you want to avoid DMUs under wires Buxton and Chester are the best options. Although, Northern don't currently have enough EMUs to run Hazel Grove-Manchester as electric even if it was split.
DOn't get me started on that at the moment, them 317s down in store at the moment could come to Northern and take over the electric parts of some of the services that run through Piccadilly. Personally I think we can live without a Stockport - Bolton service for a year or so so that we can basically double the length of Diesel services from Bolton into Oxford Road...
By terminating the Airport - Southport and Hazel Grove - Preston services short at Oxford Road or Piccadilly and interworking them, one can save at least three diesel diagrams, put these on to make the units longer and happy days, we have more seats where the're needed in both directions, with 317s taking over the Hazel Grove route.
When the electrification IS complete I think we need a major shake up of routes to be able to send all the class 142s to the cutters torch, assuming an optimistic electrification for TPE North (Leeds - York via Micklefeild, Micklefeild - Hull via Selby, Selby - Sherburn, Leeds - Castleford - Sherburn (Diversionary Route)) and comited electrification elsewhere.
Things like...
Ending through services from Wigan Wallgate to Victoria via Bolton, 2tph shuttle in place
All Kirkby and Southport services via Atherton (Giving them 3tph)
Minimum 2tph Wigan - Manchester via Paitcroft (Victoria / Exchange)
No Diesel Stoppers via Stockport, 2tph Crewe / Alderley Edge and 2tph Hazel Grove, 4tph Diesel flighted with these (Buxton 2tph, Sheffeild 2tph).
No more stupid extensions of short formations to Manchester Airport, send the biggest diagram available from that route, this could mean Southport loosing it's link.
Services via Castleford replaced with an EMU stopper to York, flighted with a DMU Semi Fast on the current service.
Victoria Turnbacks and Bays: Add in bay platforms from the Chat Moss Lines (Grade seperated at Ordsall Lane) and turnback sidings between the lines feeding 5 and 6 from the East.
Priority to EMU routes, from Bolton for example there should only be 2tph DMU Maximum, (Lakes & Clitheroe, or 2tph Clitheroe), all other services should be EMU run, 4tph to Preston or beyond and 2tph shuttles (slow services) minimum.
You can see where I'd going with this, through journies will be lost, but minimising diesel under wires, and adding in a few 'shuttle' services off the mainlines that would actually be suitable for pacers, even Class 142 units. (Since there is enough space on all the platforms between Bolton and Wigan for the ramps, and you can just lock the toilets out of use, DDA; solved...)
PS: When electrification is complete, Hazel Grove - Preston returns to normal...
There would be 4tph slow arriving from Stockport and 2tph from Airport on the slow lines to slot through 15/16 to somewhere, with Wigan (via Paitcroft), Liverpool Lime St via Newton Le Willows and Bolton providing the only electrified options, it would be logical to send 2tph to each.
But then we're looking at a very congested route through Oxford Road.
6tph Slow lines EMUs. (2tph Liverpool, 2tph Wigan, 2tph Bolton, Proberbly Blackpool N)
4tph Airport via Cord. (2tph Leeds via Diggle, ?1tph Leeds via Halifax, ?1tph Sheffeild via New Mills / Leeds via Halifax)
2tph CLC Semi Fast (1tph from Norwich, 1tph from Cleethorpes)
2tph CLC Slow (Terminating at OR / Piccadilly)
1tph Scotland via Paitcroft (Extension of a service off Euston anyone?)
1tph Southport via Atherton
16tph is do-able, just...
PPS: The way I'm pathing these up, it MIGHT be possible to run the CLC Slows with services off Stockport flighted in the slow lines, but I'd personally be moving these into the fast lines to terminate in the main shed (Buxtons) where the Liverpool L St via CLC Semis (EMT) would also be flighted behind an EMU stopper, they would continue onto the main shed, and be replaced on the slow lines by the Airport Slows at Slade Lane. This would allow a 'swap round' between paths at Piccadilly, as two EMUs will arrive at roughly the same time, and one wishes to keep 30min frequency on each, within dwell times, these can swap over, so 1tph from Hazel Grove goes to Liverpool and 1tph to Blackpool, and vice versa with the Airport. Wigan in this situation would be stuck with Crewe / Alderley Edge.
Oh and yes, I am providing 4tph to Levenshume and Heaton Chappel, it just fits nicely. More can be provided on the Styal Branch by stopping random other services at subsiquent stations on route. Usually East Didsbury and Heald Green (the busyer stations).