Might not the solution be something more like the Northern steam hauled service a few years ago to promote the Settle - Carlisle. Not a full blown heritage operation, but a way of promoting and getting more passengers onto otherwise lightly used lines. Seeing as this is a speculative thread, I am going to assume TOCs have effectively been abolished because I dont think the idea could be made to work with the current set up. GBR are running the trains. One could then imagine some heritage trains moving around the country and putting in regular appearances on suitable branch lines, maybe for a week at a time. Replacing the normal rolling stock on some diagrams, or maybe running as extras, before moving on to the next branch. The big attraction of the Northern event was it gave the possiblity to experience steam haulage at regular fares. No doubt there would be problems, but given a will I am sure they could be resolved. Try and find a suitable branch lines in each area, and go for a range of heritage stock, steam, diesel, even electric on branches that can support it. It will get people thinking and talking about the railways, and perhaps encourage greater use.