In the short-term, I’m sure that coal sourced from abroad will continue to be available for heritage use, including steam traction on preserved railways.
However, as time goes on, the whole concept of the burning of coal will be seen as socially irresponsible and will probably become a deterrent and obstacle to many members of the public when considering a visit to a heritage railway.
The steam movement must use the next ten or so years to evaluate alternative forms of fuel and begin a rapid programme of conversion. The Grand Canyon Railway in Arizona have successfully converted their two steam locomotives to run on recycled cooking oil, a source of power which is both sustainable and hugely less damaging to the environment. But we need to start NOW, and to carry on restoring (or even building new!), locomotives to run on coal is just burying our heads in the sand.
Conversion of locomotives to operate on sustainable and less polluting fuel could generate a good deal of favourable media coverage, and promote a positive attitude to the wider public.
If we continue to rely on smoky, anti-social highly-polluting fossil fuels there is every chance that steam-operated railways become stigmatised as just ‘selfish old people playing trains’ with a very negative perception.
There will still be a role for coal within heritage railways, but perhaps just a large pile of the stuff as part of an interpretive display, and perhaps with the occasional small tank locomotive on display in light steam to show visitors as a living reminder of the distant past.
We must embrace new ideas and look forward to ensure that the past has a future.