I've seen larger rotisseries used in body shops for rebuilding cars.
I think you could sell at least a few. We're not the only group of old sewing machine enthusiasts out there. There's ISMACS and some yahoo groups that I know of off the top of my head. I'm sure there are more too.
Even people who can make their own might buy if it's available. It frees up more time for machines instead.
I'm not sure what professional sewing machine repair shops use but there may be a market there as well.
Your rotisserie can save a lot of wear and tear on a machine. I know I'm flipping the machine I'm working on right now over a lot.
Rodney