Has a bike been made with a rear derailleur above the chainstays?
The derailleur needs to guide the chain into the sprocket - which means it goes on the bottom.

The tension pulley needs to go on the slack side of the chain - which again means it goes on the bottom (the top side of the chain loop has the drive tension).

If the drive train was reversed, you could do it. Put the drive wheel in front and steer with your butt - like this.

US Patent 6588786 has what you've described. Bonus: you don't have to steer with your butt - cables link the handle bars to the forks. I found this while googling for 'front drive bicycle'.


Here's another configuration: