I have to agree, planning a new high speed line is pointless, and will not happen (as in boots on the ground) in any foreseeable timeframe. Like it or not, HS2 has killed off any future high speed rail projects in the UK for a generation.
To be honest the distances dont lend themselves to proper (~180mph/300kph) high speed rail, Liverpool Manchester is under 40 miles, Manchester Leeds is 45miles and Leeds York is just over 25 miles, which is the main transpennine northern route. Aim for a 100mph railway.
4 tracks where it can be delivered without significant demolition, e.g. east of Leeds - Crossgates, 3 tracks from Huddersfield to Marsden, maybe as a reversible 'overtaking track', and the big one, get the electrification finished.
In the wider picture on northern (as in area not TOC) routes, if more capacity is needed it needs to be delivered by longer trains not increasing frequency. There are still far too many 2 and 3 car trains running on a network that is 'at capacity'. For the Newcastle - Liverpool service this needs a minimum 8 car service hourly as a 'proper' Intercity service.
That then leaves the issue of Manchester City centre, the current arrangements are a bodge, that has evolved over many decades, and is now not fit for purpose. Short term use the space beyond Platform 1 at Piccadilly to create maybe two more platforms for services terminating from the east. Dont try and run TPE on to the airport, operationaly its a pain. Run the airport service as a self contained shuttle from a pair of dedicated platforms, maybe 10/11
That then leaves Castlefield, I agree that a tunneled east west route, connecting the routes from Stalybridge and Rochdale with Chat Moss and CLC routes to Liverpool and possibly a spur to the airport is the optimum choice, retaining Castlefield for local services, but in the current climate that seems like pie in the sky. Even the proposed Platform 15/16 at Piccadilly and associated Castlefield improvements seem unlikely
Given the wider political and economic situation I would be very surprised if any funding is forthcoming in the next 5 years or so. No doubt lip service will be paid, but as for any actual work starting beyond that which is currently in progress (Dewsbury - Huddersfield), I just dont see it happening.