Well, given the massive loadings coming in from Cornbrook now and that we're fast running out of space on and soon to be placing more services on the OR Corridor, with service levels at saturation on the Metrolink too, it could seem sensible to re-open Central Station as a Metrolink terminus for some services (Notably Tram-Trains to Warrington via Lymm and on the Mid Cheshire IMO, and the CLC line services, that could accomadate a massive frequency increase to join up with Merseyrail services)
If a connection could be put into place from the Windsor Link and Chat Moss route onto the Central viaduct near the A57M, there is a reasonably clear alignment, would need more viaduct though. Then re-opening Central and running less services through Oxford Road would be a reasonable idea. And would allow an increase in frequency and destinations to the West of Manchester to a nicer service level, and take some pressure off of Victoria for Westerly terminating services.
If this Chat Moss and Windsor Link where plugged into Central than IMO the Metrolink extra platforms / capacity should still remain souly with the 2CC and a plan I formulated before for 2 platforms for Metrolink at Oxford Road station as part of a re-build.
Realistically, changing metrolink back to heavy rail would take an auful lot of effort, including new track and viaduct from Panoma to Old Trafford, so that the East Dids / Chorlton Lines can have access with the heavy rail lines running to Alty.
However, if this tram/train concept can be sorted out and electrodiesel trams provided that could run out onto heavy rail lines then there are a number of routes that could be re-opened and additional capacity could be added to this part of the network by re-instating some four track and limited stop metrolink services running. This however would need Metrolink's Tram/Train operations intergrating into the ATOC.
If the tram-train idea works then an extra few tph could run to down the alty line and onwards to the likes of...
Chester via Alty
Crewe via Alty
And with some re-openings?
Warrington via Lymm (Street running where needed)
Chinley via Didsbury
Or borrowing some Heritage Railways?
Victoria - Rawthenstall
Bury - Rochdale
So expansion of metrolink outside it's borders with 'shared services' run by a TOC that is part of ATOC over say, the Mid Cheshire Line or other re-opened routes, or forcing Metrolink to join ATOC and work as a TOC (pleeassseee....)
And if these tram-trains (from the Cornbrook direction anyway) had somwhere like extra platforms at Oxford Road to terminate at, rather than running (potentially 8 car trams, I'd invisage fixed 4 car formations) onto the Metrolink lines in Manchester CC) then it would take away some of the congestion there.
Back onto topic anyway, Central, Would be very handy today for terminating these additional tram-train services should wishful thinking prevail and they can run on 25KV OHL, 750V OHL and Diesel. Combined with being used for the CLC line terminators.
Note that if Central was being used, the long distance Tram Train services would make use of four track wherever possible and run fast, only calling at Cornbrook, Sale, Timperley and Altham (with the 1 track section being intergrated into either Metrolink or Network Rail and a fully shared station built).
With Cornbrook rebuilt to provide access from the CLC to the two 'Central Station' lines, and the Metrolink Lines able to access these lines for their services to terminate from long distance routes, services using Central could be numerated to...
3tph Chester via Alty Mid Cheshire Line
2tph Crewe via Alty & Middlewich & Sandbatch (New station there)
2tph Warrington via Lymm?
2 - 3tph Chinley via Didsbury (Additional platforms on the line from Hazel Grove, calling Cornbrook, E Dids (Some 4 track added), (Wherever the Stockport CC Line Splits), Edgely Road, Bramhall Lane, Hazel Grove South, Chinley
2tph Semi Fast Liverpool Lime Street - Manchester Central (As current fast patterns)
2 - 4tph Slow Liverpool Lime Street / Central - Manchester Central
That would give Central 10 - 12tph Trams and 6tph Heavy Rail
And free up 4 paths on the Oxford Road viaduct, or two paths if only stoppers are diverted (and additional semi fasts still provided, giving the CLC up to 8tph)
Much more potential for services if there is a route from Ordstall Lane to Central...
Somthing to Buxton maybe?
And running into Victoria and either down to Piccadilly, or using some new platforms there...
2tph Rawthenstall - Vicroria?
EDIT: And as somone sudgested, the Fallowfeild Loop, dual voltage trams from Piccadilly to Central via Fallowfeild? 4tph