Do you think the tempest cooling unit could be used as a mouthpiece to add cooling?
It could be used but for my own use I don't use a cooling stem when I'm using a water piece. That's kind of redundant and unnecessary to me. I generally feel it's only worth the cleanup necessary in a cooling stem when I'm using it native without water. I might use it if I were using a dry glass piece, but I don't generally use dry glass.
Added: The cooling unit for the revolve and the Tempest are very similar, with the Tempest virtually being the Revolve Gen 3. I think the Tempest stem cools a little better, but that might be in my head. Here is a Revolve gen 2 with a wood stem using the Revolve cooling unit.
I absolutely prefer the substantially longer application of heat that the tempest provides, but I still occasionally use a VapCap tip and cap instead of the Tempest head. They are pretty much interchangeable as regards the fit.
I do intend to get a wood stem made for Tempest when I get my updated parts and second head.