Duke Nukem already has several side-scrollers... '3D' was actually the third installment, and a popular naming convention at the time (many games with two 2D installments developed a third in 3D) to make a double entendre of the '3' suffix).
If we would do another "mini-game" it would probably be mini-quake haha... But right now we are trying to make an original game. Making fan games is fun, but it doesn't pay the bills :(