My personal preference for northern TPE would be to drop out one service per hour across the core and lengthen everything to 6 carriages. Same for anglo-Scottish in terms of another carriage. There is bags of demand at all times of the day and that may well build further. However, the unreliability of the infrastructure is not changing anytime soon and Manchester is a mess. The current number of diagrams per hour can't be sustained and this is before the other Manchester mess, the airport station, needs to turn around longer trains.
Performance through the core has been poor ever since the 5th TPE train (Liverpool - Newcastle) was introduced (in 2014 IIRC?). The May 2018 timetable (6th TPE train instead of the Northern stoppers, skip stopping, Scarborough - Liverpool rerouted via Victoria, Airport trains rerouted via Ordsall Chord) was supposed to improve punctuality, but made things much worse. The subsequent timetable changes (including the forthcoming Dec 2019 timetable) have just been "sticking plaster" tweaks (longer turnarounds, split stopper, stopping pattern changes, increased pathing allowances). I believe the longer term plan is to link the two stoppers into a 6th through train again - back to the future!
TPE and DfT/TftN need to recognise they are in a hole and stop digging! This timetable is never going to work reliably over the current infrastructure, and the new, longer trains with end doors may well make punctuality worse. IMO the core service should be cut back to 4tph, plus the stopper, pending the TRU enhancements.
Of the eastern destinations, Scarborough seems to be the most vulnerable to delays and cancellations, so I would suggest it gets an hourly shuttle to York in place of the through service to Liverpool. At the western end, the Castlefield corridor is the main problem, so one of the Airport services should be culled. This would leave 1tph to the Airport via Victoria and the Chord (from Redcar?), 2tph to Liverpool via Victoria and Chat Moss (from Newcastle and Edinburgh?) and 2tph to Piccadilly via Guide Bridge (from Hull plus the stopper?)
This reduction in frequency would probably mean continued overcrowding through the core, even with all services 5/6-car. So TPE should explore options for lengthening the 802s and Mk5A sets.