My friend and I were chatting about this last night. I have seen a lot of posts on here about the hellfire rings, and that they aren't that great. Unless you get a good roll or enchant as I take it with most items. The keys are also much harder to get unless you're farming T6. My friend said it would be cool to give you a nice bonus shard, like 200 for completing an UBER event. Just seeing what other people think about something like that, or any other cool thoughts for some more end game stuff in the future. I think this would make playing UBERS worthwhile if there was something else besides just the ring. In the past I also thought it would be cool to get hellfire gear in general. Although, that might be good or bad depending.
Something similar to the Ring of Royal Grandeur, or maybe a crafted Amulet that is class based with a random class based skill that activate all runes. Unless they could implement the Uber Charm like the old days