Original Q&A summary:
Non-VEX LCDs are legal provided they do not display anything related to the state of the robot.
Emphasis added by me.
Would it be correct to interpret <R7>d as prohibiting “functional” use of non-VEX LCDs only during matches and skills runs?
Or must non-VEX LCDs be limited to “nonfunctional” nature for the entirety of an event, including time in the pits and practice fields?
For example, would this be legal:
When the joystick is plugged in to field control, the non-VEX LCD is automatically put into a “nonfunctional” mode that displays only static images, non-robot-related animations, etc. When not plugged in to field control, the non-VEX LCD displays sensor data. A manual override would be used to put the non-VEX LCD into “nonfunctional” mode should the robot fail to do so automatically for a match or skills run.