Motor controller

[Andreas29]

Why you don't try simply connect the nano to the pi zero via usb ..... no other connections to the nano than usb !
save sailing
Andreas

I'm curious why this is not the standard or at least more common?

Are there code changes that have to be made for the pi0 to talk to the nano via usb?

Hi,

no code changes. 
When testing with "flying wires" it´s a common way.
When using a pcb imho it´s better to use the connection via the gpio then via usb. The needed connection is printed on the pcb.

Regards

Andreas