The wall-framing takeoff could already size a deck's stair from the deck surface height, but only from the command line. The page now has a "Stair down to grade" select in the deck card. Choose Yes and the stair uses the deck height as its total rise, with a 10 in tread, 2x12 stringers and 36 in width (the CLI defaults). A separate stair card still wins if both are on.
Checked by the page's source tests and the existing stair engine. Not checked against a built deck.