I've seen a few home-spun suggestions in past months, but can't recall much detail about them. I think there's a full solution in production somewhere on the 'net that sends a signal to the controller to pause when a filament out is detected.

I've got my mind set to build something similar with a mouse wheel and detector pair, plus Arduino or similar simple processor to detect not a broken filament, but a lack of movement over a period of seconds. My bowden-tube extruder can have a failed print without broken filament, but it will always stop moving the filament. It would be great to have that or similar option available.