I was looking through a Network North West timetable from May to September 1990 and counted 14 passenger trains an hour along the Castlefield corridor during peak times. The main difference back then was most trains were fairly 'local' (Liverpool, Blackpool, Wigan etc) with the exception of the Sheffield (and beyond) - Liverpool service each hour.
The issues along Castlefield only seemed start when the TP Express Scotland and North East services began going that way, bringing with them their delays picked up at other bottle necks.
Scotland-Manchester is the key market. Then it's easier to carry on to the Airport anyway.
I've yet to see a proposal to divert it to another termination point that doesn’t either require infrastructure or create a capacity problem.
14tph through Castlefield
in the peaks may have worked reliably in 1990, but more has changed since then than just the mix of local and long distance services. Much bigger passenger flows (pre-Covid), longer trains and infrastructure changes, e.g. Ordsall Chord and Manchester Airport station.
A reliable 15 minute service around the Ordsall Chord would be the ideal solution to connectivity between Victoria and Piccadilly, and indeed was the raison d'etre of the Chord. But is very difficult to see how it could be accommodated without the complementary part of the original Manchester Hub plan, namely four full length through platforms at both Piccadilly and Oxford Road.
In all three options of its near-term timetable recast proposals (with no infrastructure enhancements) the Recovery Task Force has kept the existing 2tph Airport - Redcar/Newcastle trains as the only services on the Chord and also retained the 1tph Airport - Scotland and 1tph Airport - Cumbria services through Castlefield. More drastic changes to the long distance services would be the only way to get a reliable 15 minute local service on the Chord with the existing infrastructure.
Network Rail experts have calculated that the off-peak frequency through Castlefield should be limited to 12tph, including the 1tph freight path and the locals that reverse at Oxford Road. As well as the 4tph on the Chord, all the 5tph (including the freight) on the CLC line must go through Castlefield. So that leaves only 12-4-5=3tph total that can come from the other three lines to the west - Chat Moss, Atherton and Bolton. Everything else has to go into the four through platforms at Victoria, in addition to the 4tph from the Chord.
I would choose electric services to go through Castlefield, because otherwise they would clog up Victoria reversing in the through platforms. So 2tph from Blackpool and 1tph from Glasgow/Edinburgh. And I would get rid of the N Wales service as in the Task Force Option C, by sending it round to Piccadilly via Northwich and Stockport.
I think the 4tph fast service to Leeds, York and beyond would have to be sacrificed - others have suggested rerouting 2tph to Piccadilly via Guide Bridge, but I doubt there would be sufficient platform capacity. So strengthen the 2tph Liverpool - York services to 9-car 802s instead, with 1tph Hull and 1tph Huddersfield services remaining on the Guide Bridge route from Piccadilly.
Then, assuming the same Atherton and Bolton frequencies as in Option C, we are left with the following off-peak services into Victoria from the west:
4tph Ordsall Chord
2tph Liverpool via Chat Moss express (to Leeds via Stalybridge)
1tph Liverpool via Chat Moss stopper
2tph Chester via Chat Moss
1tph Kirkby via Atherton
1tph Wigan via Atherton
2tph Southport via Westhoughton
1tph Clitheroe via Bolton
1tph Blackburn via Bolton
1tph Cumbria via Bolton
Total 16tph, versus 12tph into Victoria in the baseline timetable, so problematic!
I would send all four Chord services through Victoria Platforms 3/4 to Stalybridge (with short turnarounds), in order to minimise crossing movements between Deal Street Junction and Miles Platting Junction, so maximising capacity and reliability. They would slot between the Liverpool - Leeds expresses and could become electric once the wires to Stalybridge are up. The electric Liverpool stopper could use the reversing siding west of Victoria to clear the platforms during layover. The diesel Cumbria service could run ECS to Brewery Junction and reverse in the loop. That still leaves 8tph to run through towards Rochdale or reverse at Victoria.
2tph (from Chester) can go to Leeds via Bradford.
1tph (from Wigan) can go to Leeds via Brighouse.
1tph (from Kirkby) can go to Blackburn via Burnley.
2tph (from Blackburn/Clitheroe) can terminate at Rochdale.
That still leaves the 2tph from Southport. Not sure if they could be reliably squeezed into the single Rochdale bay too (the Clitheroe service currently has a 14 minute turnaround time). But reversing in Victoria Platforms 5/6 would likely cause too much congestion.
Not easy - can anyone do better without infrastructure enhancements? I still prefer the Task Force Option C.