Using "" rather then "" would be needed for accessing ip cameras.  No point in limiting the usage to locally attached devices.

What happens if it's a USB webcam and the network is down for maintenance?  I'd be wanting Motion to record the burglary locally, without caring about the state of the network.

I'd also want to keep it in a chroot environment.

Can you explain your reasons for wanting this?  I wonder if the Motion developers are even watching this thread.  Maybe I need to create a Feature Request on the website as well.