I think the point is being missed here, unless you have deep pockets experiencing steam traction is pretty much restricted to heritage railways. I for one would not want to lose that opportunity to interest and educate people. Its part of history and its hard to price on it, but in the same way as goverment funded major museums like the NRM contribute in ways which it hard to quantify so do heritage railways.
The NYMR are looking into oil firing, as an easier way to operate steam engines, and when experiencing a dry spell have to revert to diesel traction anyway owing to the fire risk.
For the larger operations I dont see any of them abandoning steam, thats one of the reasons for their existance.
I also take issue with people who prattle on about the environmental impact of heritage steam engines, its a tiny contributer, how many tons of coal does the whole UK heritage industry use in one year? I suspect one senior politician contributes as much CO2 in a year from their air miles as one of the large heritage railways. Tell politicians they have to pay for thier own jollies and I best the 'carbon footprint' of the average politician would be negligable. I also believe that we should retain at least one strategic source of coal mined within the UK. Recent events in Scunthorpe confirm that things can rapidly go out of control.
We really are bad at going for the low hanging fruit, with talk about 'decarbonising' a route like the far North Line, while diesel engines are being used on a daily basis under wires, and there are still large sections of the intercity network that are un-electrified. And as for moving passengers and freight to rail from road, most of the recent events have been going in the opposite direct, fares now considerably higher than the cost of driving for example.
A bit of a rant... Sorry