Yes, but the L&MR was not exactly under-engineered considering it might have been horse or cable worked and is only realising it's full potential now with electrification. In many cases capacity was doubled once the demand became apparent, as you say Stockport viaduct was widened, most of the Standedge route became 4 track if we include the Micklefield Loop etc. I cannot see capacity enhancements happening on this scale today even though there is clearly a great deal of suppressed demand, in particular for Trans-Pennine journeys and suburban and regional traffic to and from Manchester. Most of the capacity which has been stripped out over the last 50 years cannot easily be put back because land has been sold off for so called 'development'. Furthermore, as a previous post indicates, the obviously necessary grade separation at Ordsall/Windsor Jcts is impossible or ruled out because the land is worth more for even more property 'development'. All this 'development' increases demand on already overstretched infrastructure. Perhaps there should be a compulsory levy on all 'development' to pay for infrastructure investment, and not just railways but also electricity generating capacity, water supply, sewers etc. but I suppose this would not be considered appealing to investors in a "Britain open for business"....just bang up the properties and take the public infrastructure for granted!