Converting Glossop/Hadfield to tram or tram-train would be a huge mistake IMO. It's a high quality electrified suburban railway with relatively modern rolling stock and equipment that still has plenty of life left in it, so any conversion would be viewed as a downgrade. The Bury and Altrincham lines had elderly units and in Bury's case non-standard equipment, so conversion made sense. The Rose Hill line, being a diesel stub, would make sense to be converted... particularly as the route previously ran through to Stockport and possibly could do so again as a tram line.
Sensible thinking.
The financial advantages of Metrolink to a parsimonious central government, and relatively cash-strapped local authorities, have led to swathes of the heavy rail network being torn up, regardless of the reduction in per-vehicle capacity (and speed), and the effects on the wider network (in particular, the loss of the direct line via Sale to mid-Cheshire, and the impediment to re-opening a line to east Lancashire via Bury), exacerbated by cretinous and unnecessary features such as the single tracks between Altrincham and Timperley (which, if the line via Sale had to be stratified, should have had some form of track sharing between heavy and light rail from the outset). While someone will remind me that the trams run more frequently and cheaply, and avoid the chronic and acute capacity problems of the central Manchester network, this underlines the extent to which they are an inadequate substitute for the heavy rail suburban / metro system a conurbation the size of Manchester should have (albeit it now seems we need a city centre underground anyway due to tram numbers, negating much of the advantage of light rail conversion). I hope that we will eventually see many of the Metrolink lines being converted into that sort of system when the heavy rail network finally receives the investment it should have.
Anyone who has been at Romiley at the morning peak, watching 4 car DMUs at 10-20 minute intervals leaving passengers behind, would seriously question whether 6 trams per hour could deal with even existing demand on these lines. This is before we even consider the wisdom of closing off 1 if the 2 lines between Manchester and Sheffield to heavy rail.
This is not to say that Metrolink does not have some very useful roles. Some of the lines (eg Salford Quays, Traffird Park) penetrate areas unreachable by heavy rail. Rise Hill Marple is another example of a potential use, a stub end (though still fairly busy) diesel service which could usefully be extended further along the old trackbed and beyond eg to Hazel Grove, providing the aort of link between peripheral areas which is badly missing in Manchester (and virtually all our other cities). Perhaps in the other direction it could connect to the Ashton line, rather than taking up any capacity on the Guide Bridge formation.
