I'd love to be able to see the project planning process for Stonehenge! 100 years ago the Swiss did well to drive a tunnel up and through the Eiger to Jungfraujoch, a location with a human population of zero. That has been a success - just to go up a mountain and come back down again.
But my mind is drifting. Major projects in this country tend to run into the problems of democracy. I and my group want to do it, you and your group don't. After much consultation, public inquiries and lobbying I get my way and it's decided it will be done. But then it's far too expensive and you've won. However a third way is identified. I get half of what I wanted and you get half. The money gets spent and in 10 years time we can't understand why the whole job wasn't done properly in the first place. Another 20 years later it's finally done in full having cost 10 times what it would have cost at the start - and kept irritating the local populace for 30 years instead of 10.
I remain convinced that the long term best solution is a tunnelled express network beneath the centre of Manchester out to the edges of the built up area. The Romerike Tunnel in Oslo is over 9 miles long from the city centre to the outskirts. It went 3 times over budget, proving such projects can go wrong anywhere, but it gives impressively fast journey times into the city from the airport.
Bite the bullet and go for it. Lines leading in from all points of the compass leaving the surface tracks for more local services. Once the underground box, wheel or circuit is built it will be marvelled at how we managed without it.
If you were going for really big you could build the platforms mid point between Piccadilly and Victoria with travelators bridging the ~500m gap at each end. Ideally with more to give access from other areas and to give access to the middle of the platforms too.
You could then have multiple surface access points and you'd be able to use the travelators to get around the central area of Manchester.
They wouldn't be quick, but with no waiting time there's a chance that they would be quicker for short journeys (i.e. you probably would go Piccadilly Victoria on them but would use them to go one or two tram stops).
It would reduce the number of surface rail services, reduce a little the capacity demands on the trams, reduce the walk distances from rail to many locations, make public transport the go to option for more people, etc.
Yes it would cost a lot. However if you could reduce the need for car parks in the city and increase the attractiveness of the area for development it's possible that you could increase tax takes (i.e. council tax, stamp duty, business rates, etc. - not from them being higher just from there being more).
At the interchange between walkways you could have double level public realm spaces with shops, cafes, green space and maybe even children's play equipment.
Such hubs could create the outdoor space which many missed when they were in lockdown in their flats.
The new station would cater for the medium and long distance services (XC, TPE, HS2, Avanti), however the capacity it created would likely be used up rather rapidly by increasing frequencies of the shorter distances services and services with a local calling pattern.
It would likely justify the TPU and NPR (whatever the maximum of that which people think we need) and could even require more capacity to be provided as rail use increases (i.e. looking more like Central London in terms of the use of cars for transport).