On servers, aesthetic builds are constantly ruined by players forgetting to seal the Miner's Delight perk. Would it be possible to add a block similar to the Cave Illuminator that instead targets and removes all Miner's Delight / Cave Illuminator light sources in a large area of effect?

Already in the "master denial" ticket. Use the illumination wand to remove them, or teach people to be courteous about playing on a server or with other people.

Also the vanilla "fill" command can be used to replace them with air.