So according to this source the new UNO Show'em No Mercy game allows for stacking Draw Cards.
Someone asked a question in the comments there and I have been wondering the same:
It seems clear to me that you are allowed to stack Draw 2, Draw 4, Wild Draw 6, and Wild Draw 10s. But can you stack a Reverse Draw 4 as well? And if so, would the reverse effect activate? Perhaps someone who owns the game and has access to the manual can chime in.