Riding is not as important to me, since I find that riding behind steamers in enclosed cars is nowhere near as fun as open air cars (which you won't see on the mainlines) where you can better see the engine, hear the engine working and smell the coal smoke (and get covered in cinders ). Of course, being in the cab is even better.
No guarantees that it will be the same, but vestibules were open on the public trips last fall. They were closed however on the private trip to Alcoa.
Hopefully, they will allow them to remain open on any future public excursions. Nothing like getting pelted with cinders at 40mph while listening to the whistle and stack talk.