You are asking about the survival of steam operations. That is actually a much too narrow of a question. Even tourist operations that utilize diesel locomotives are facing the same problem. I hear it all the time. Where will the next generation come from? Why can't we energize more young people? What we will see in the future may well be the passing of magrinal steam AND diesel operations. Economics are the greatest threat to the continuation of steam operations. With the cost of a complete tear down and rebuild for a Form-4 every 15 years now costing %300.000 to $500,000. You have to take in over $33,000 every year just to pay for your next Form-4 overhaul. That doesn't include fuel, routine maintenence, salaries, etc. Larger operations that can attract large ridership, 100,000+ per year will survive. Those that can get state or federal funding will survive. Those that can get large grants to pay contractors to do work that their fare boxes will not support will survive. Marginal steam operations will probably be the first to go, but they will be followed relatively quickly by even marginal diesel operations. 10,000 cab rides a year at a marginal operation will not turn the tide of economics. Cab rides will continue at many places. They will probably have to be more organized and regimented, but that is our own fault. Remember, lawyers don't hire themselves, we hire them after we have done something stupid. The NTSB demands a sterile cockpit on commercial flights for good reason. People flying in a Cessna don't have the same rule. You can sit right there and talk with the pilot. The Cessna pilot has to be vigilant and realize when he/she needs to demand silence and concentrate fully on controling the aircraft. The same is true of railroad operations. Most of what we do is more in Cessna operating peramatures rather than commercial operations.
The two greatest threats in my mind are: 1) there are many more potential diversions for our time than there were fifty years ago. Many people would rather spend 20-30 hours a week on the computer than to spend a day on the railroad. 2) economics. For safety reasons everything continues to become more expensive. Can we attract enough riders to support our hobby?
Big time RRs talk about rules being written in blood. The formalization of the Form-4 and its related expense is because of what happened at Gettysburg.
