Idea is to expand the beacon to give it more uses not sure of what tier these effects would be or if there should be an alternate way of getting these effects. Here's a few I've thought of:
Increase in plant growth in area. Plants with limited heights will have their limits increased by 1.5x. Sugarcane and cactus would grow to 4 blocks.
All undead mobs won't spawn in this area. If an undead mob roams into the area they will be reduced to 1 HP.
All blocks in this area will get increased hardness making it harder and sometimes impossible for tnt and creepers to destroy blocks. Blocks would also take longer to mine, but would require same tool.
Outlines mobs that are within 20 blocks from the player. This would also work on other players.
I'm sure some of these seem OP if not all of them, but I feel this is fair being a late game item. Perhaps they could all be tier 4 or have increased effects at tier 4. Maybe even have it be an addition to beacons and give these effects a timer such as fuel in a furnace.