There is no reason to invest in any of this. It is like the DRGW narrow gauge. The use of coal in electric generation is coming to an end in Europe. These trains will probably keep running until solar/wind is installed. So unless some really cheap/free diesels are offered, these steamers will continue until the electric plant is closed in the next five years.
Similar to why steam lasted until 1967 on the Waterloo lines in England, because the transition would not be to diesel but to a new electrification.