Here it is, official word from Blizzard on the highly anticipated Key Ring Function, it will be implemented in the next patch!

We're pleased to announce that the keyring functionality has been completed and will be in place for patch 1.11. When a player first acquires a key, they will automatically acquire a keyring that will hold permanent dungeon keys. The size of this keyring will increase as the player goes up in level -- as seen below.

Level 1-40 = 4 slots
Level 41-50 = 8 slots
Level 51-60 = 12 slots
~ Eyonix