Originally Posted by StephenH

I'm not sure what you're getting at, but there have been endless variations on all style bikes. For example, note that the "SoftRide" time-trial/tri bikes are upright frames that are not the diamond shape. There have been bicycles propelled by both arm and leg motion. There are a couple of problems. One is, it's a lot of extra complication and weight, so fitness may be a selling point, but speed isn't. Secondly, if your legs are in good racing shape, you're likely limited by heart/lung capacity rather than leg muscles, so adding arms to the power doesn't really help that much. On odd recumbent designs, there have been some "prone" designs, where you lay face down, head forward, which is great for aerodynamics and bad for everything else (should be some videos on youtube if you look there.) But pretty much every conceivable layout of upright and recumbent bike has been built somewhere over the last 100 years, and if a new design becomes popular, it's more likely due to better execution of the design, better materials, or better marketing, rather than just an improved configuration.