I for one would hate the idea of the player being an android; it makes no sense (stimpacks, breathing under water etc.), its not creative, and its downright overdone and cliche.
However, the one scenario that it would be cool is if, at some point in the game, The Institute captures you and replaces you with a synth. You would have to escape and hunt down your replacement, but it would be cool if you had the (evil) option of playing the synth to instead hunt down the main character and kill him.