My guess is that [1] 4 wheels don't solve the fundamental problem of lifting - counterweights (unless your 4-wheel "platform" is so wide to not easily fit / man

My guess is that [1] 4 wheels don't solve the fundamental problem of lifting - counterweights (unless your 4-wheel "platform" is so wide to not easily fit / maneuvre in the warehouse), and [2] 2 weels are enough - with modern motors, microcontrolers and feedback algorithms, 2-wheel platforms (think Segway) are perfectly stable.