Looking at the existing binary_sensor device classes, there doesn’t seem to be on appropriate for a filter which might require changing. Would be great to get a filter or similar device_class with Clean and Dirty states mapped to On and Off.
I would use this in many cases across my dashboards including recurring tasks (changing filters, vehicle cleaning reminders, toothbrush replacement…) and/or usage-monitored appliance states (Clothes Washer, Clothes Dryer, Dishwasher, etc).