I think the electronic displays have a least a 30 minute battery backup in case airplane electric system goes out. A "30 minute reserve" is all that is needed for VFR fuel, so should also suffice for electronic display.
Certified aircraft for VFR flight require only airspeed, altimeter, and compass. I think I would want those instruments for backup and then if the multifunction display goes out, the plane could still be flown even with the display removed for repair.
Homebuilt aircraft have even less restriction. For VFR flight in a homebuilt no instruments are required. You can fly with a perfectly blank instrument panel.
