I've been watching this season over and over again, and I believe I have the answer. And I'm sorry, but the clues are not in the titles. Although, the episodes where the clues are are usually character specific episodes. So far, I believe four of the keys have already been found, and I will tell you about them now. They are all related to each pony's virtue, and they are also tying into the toy theme this season, RAINBOW POWER! And that is the major clue to the artifacts. Some have been thinking too linier with the keys, that they would actually be keys, but don't you remember? When the girls had the Elements of Harmony, they looked different than when Princess Celestia used them against her sister in the past. They changed form to match the cutie marks of the girls. But the girls don't need the elements anymore, because their virtues make them the elements. And it is their virtues that will lead to the keys.
In Rarity Takes Manehatten, her generosity causes her competition to steal her designs. But Coco has issues with this, especially with the way she was being treated. In the end, Coco tells Rarity the truth, and gifts her the thread, where we see the first rainbow shimmer.
The next one is Rainbow Falls, where Rainbow Dash must choose between her Ponyville relay team, or her idols from the Cloudsdayle team. When she ultimately chooses to stay with her team (loyalty), and qualifies, she receives a medal. At the end, we see the rainbow shimmer again.
The third one is Pinkie, in Pinkie Pride. She didn't give up her partying because she thought she was being upstaged, then they threw an awesome party (Laughter) and Cheese gave her Boneless, which then shimmers.
Finally, we come to Fluttershy. No, it's not the fang, although I do believe that that may come into play again in another episode, but for another reason. No, Fluttershy's episode was It ain't easy being breezies. She learned that in order to help the Breezies, she had to do what they might now want to want to, but she had to (kindness). And Seabreeze gave her the flower, which then shimmered.
If this is the case, and the pattern is to continue, we shall soon see Applejack's honesty totem, and finally Twilight's Magic totem, whatever they may be.