I wish the Duo had seen a few arcade laserdisc ports. I know their appeal is limited, but I LOVE stuff like Dragon's Lair, Space Ace, Cliff Hanger, Cobra Command, etc.
The Sega CD got a bunch of these, plus a slew of more obscure titles like Road Avenger (awesome!) and Time Gal. I would have loved to see some of these on the Duo with its superior color palette.