I recently acquired a Surface Studio with the Dial and there is quite a bit of potential in this new input device. Here's hoping you are already well under way integrating the device and these ideas are old-hat.
One of the great uses of the Dial is for controlling the Undo/Redo stack. Suggest tying History to the dial for a quick way to scrub through your actions.
Brush Size, Flow, Opacity are also natural properties that would work naturally with the Dial.
One of the nicest surprises with the Dial is in Microsoft Ink Workspace - there is a virtual Ruler that can be placed and oriented with the dial that also locks your stroke. This is such a great feature for perspective drawings and would love to see something similar for placing guides.
Scrubbing through Brush presets is also a welcome feature in Microsoft Ink Workspace - it only supports the 3 built-in brush types, but if Photoshop could allow for selection of a few favorited brushes through the dial, it would be very nice.