Despite doing full clears of all areas, all possible quests, and getting all but two achievements, I never did find a use for the key on the chandelier in the Maxos' Temple round stairway. This both in DK:ED and DKS.
There were rumors in DK:ED that the key might have been for a half-buried locked chest in the northwestern room of the area with the locked door and hidden levers, but I could never unlock the chest with the key, and in DKS that chest is no longer locked.
I'm going to ignore the key next time I pass through there.
