The last film I saw in 2x3 sheets was Kodak VPS back the the mid 80's. Meisel used to process it back then. If anyone is doing it today would be using a dip & dunk line. Jobo also had a reel that would hold the sheets.
I'd say the demand is zero for the reason you mentioned - 120 roll film. The cost of doing eight sheets of 2x3 would far exceed the cost of doing a roll of 120.
I process 2x3 B&W. I have reels that hold it as well as SS hangers. Reels in tanks are much easier.