It may be no understatement to tell someone that all that can be possibly tried out with bicycles have been already tried. I wonder how much is left to do? Maybe 2%? Okay. 3%. I suppose that the probability that your new bicycle idea is unique compared to what's come and gone is very small. I hold the theory that given something that is really popular among the masses, and a lot of time span in years, that probability gets even smaller.
Here are a few of those ideas from history. The creativity is compelling. More here for your weekend pleasure.