If we are getting consideration of new paths through the Castlefield corridor. I think no cheap fudge will do.
Manchester clearly needs a new East/West rail link - preferably one that supports NPR HS3 as well as other traffic. I think this needs to underground (a sort of mini Crossrail) with a new Central Manchester station at least 4 tracked to the throats and then 6 or 8 through platforms - so that say Preston trains are always on Platform A, Liverpool trains are always on Platform B etc.
At present we are getting lots of expensive proposals addressing a range of options (e.g. speeding up Manchester Airport - Yorkshire services by rerouting them through Victoria (always seemed a daft idea to me), Removing terminating services from Piccadilly and Oxford Road in favour of commuter focused through services e.g. Liverpool to Crewe stoppers, Platform 15/16 at Piccadilly, Oxford Road capacity issues, NPR HS3, Phase 2 of HS2 already with a proposal for a long tunnel access to a new Piccadilly station) each being looked at in isolation and promoted by different interest groups.
I think it would be far more sensible to bite the bullet and decide to do a single major project. If cost savings are required, a rerouting of HS2 so that it approaches Manchester from the West would obviate the need for the separate Airport to Ardwick tunnel.
Interestingly there is already a lot of underground infrastructures in Manchester (for example the disused Manchester and Salford Junction canal tunnels run from Castlefield basin to underneath Manchester Central on an alignment that if continued would pass close to Piccadilly - although probably not deep enough and in parts not wide enough for this purpose). A station with platforms long enough to accommodate HS2 trains would near enough stretch from Manchester Central to Piccadilly anyway so access could be at both ends.
Such a proposal would leave the existing Platform 13/14, Oxford Road, Deansgate/Castlefield corridor for commuter, freight, and any residual diesel services only.