Well at today's high excursion prices, I would probably say...not much demand. Why you ask. Well because it would probably cost more to do this at night these days, after all where are folks going to sleep. Unless you use coach seats you will have to charge more for sleeping cars perhaps. If you go with coaches, then I suspect it would be fine. However, you would probably lose all the regular quasi-fans who just want a day out train ride, cause they want to do it during the day. Interesting concept, that might be worth exploring. The oddity of it just might sell. We talked about that on the C&TS for example and many expressed interest in riding at night, although I am not so sure how thrilled the crews would be running through the gorge at night!
I always enjoyed those late excursions in the 80's on CSX of NS where you could hang out the vestibule dutch door and hear the engine blowing for crossings and such at night. That was fun.
Greg