I bet it cold be done with most of the work being done on the machine side. I've accidentally launched a zoom type window around my mouse on my Windows and Linux machines. I bet it's an accessibility option under a hot key.
PING located by webcam,
PING checked every 2 seconds by Arduino,
If clearance in front of the machine drops under 18" send a "ZOOM" request to the serial port,
Insert fancy computer programming here that listens to the serial port and makes the ZOOM happen,
If clearance in front of the machine is greater than 48" bump volume up a bit.
If the statements become false back out....
I would even bet that you can manipulate the properties of the zoom window to your liking (bigger, smaller, how long it lingers, etc)