In case you missed it, Sylocat commented on Saturday’s liveblog post with an excellent theory on what’s going on in the current season of Friendship Is Magic.
To summarize, the theory is an elaboration of the by-now standard fan theory that the rainbow-sheened objects the Mane Six are accumulating are in some way the keys to the crystal chest from the season premiere. Sylocat’s expansion is that these items represent a moment when one of the Mane Six was not only the epitome of their own Element of Harmony, but brought it out in someone else. So, for example, Rarity’s rainbow thread exemplifies not only her own generosity but the generosity she brought out in Coco Ponel.
I like this theory quite a lot, and think that thus far it fits pretty consistently with the events of the season. I think it also meshes well with my own theory, which is that they’re in the process of creating new Elements of Harmony that do not require draining the Tree of Harmony.