If a Lux sensor gets rid of another multisensor (that would be at least be doubling up on motion, and temperature) I think it would certainly add value.
You wouldn’t even necessarily need to have it displayed on the ux/ui right away. For Example, BloomSky Weather Station’s have a rain sensor. The app doesn’t display anything about rain. It does however send a push notification when it is raining. However using their API you can ask the device if it is raining or not. The created st app does have a tile for this sensor, and the user in this case would have the choice of displaying it or not. This is helpful in a like manner to adding a lux sensor.