I think that reactions will generally be positive. It's still a steam engine, it still looks and sounds the same from the passengers perspective, and it will still produce the expected black smoke on steep grades. I think most will welcome the fact that the train will be cleaner from the moment they get on, and folks riding in the open cars will not have to deal with cinders in their eyes, which can positively ruin someone's day, especially if they wear contact lenses. About the only ones who may complain will be railfan chasers, because many of their photos which used to feature a little smoke will probably show a clean-stack, unless there's a decent grade. Charter patrons will still get smoke.
With regard to passenger expectations about how steam engines are fueled...... I have been to a LOT of steam operations all around the country and talked to a lot of patrons, many of whom really don't understand much about how steam engines work. But the vast majority of them do assume that steam engines are fueled with coal, regardless of what the particular railroad is actually using. Oil firing is a mystery to most people outside of rail enthusiast circles.
/Kevin Madore