In one word, Change Your Mind was amazing. So amazing that I spent three hours on the Steven Universe subreddit after the episode ended (which also means a lot of my ideas were influenced by the subreddit). To me, it was the perfect conclusion to the past five seasons of the show. Steven Universe has changed so much since its first episode, and yet at its core has stayed the same throughout everything that has happened.
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Steven Universe is a family show. It is fundamentally about family---Steven's family. At first this was the Crystal Gems, and then now we see this family extended to the Diamonds. Blue and Yellow's sudden change of mind may seem rushed, but in the context of family it's understandable. Communication is key, and before Change Your Mind there was little communication between the Diamonds. Steven changed that by standing up for himself and confronting Blue. While Pink decided to run away from her problems, Steven was able to face them. He made the Diamonds' flaws apparent, allowed them to accept their imperfections. As a wise man said, If every porkchop was perfect, we wouldn't have hotdogs.
Identity is a major theme in Steven Universe. Even in the beginning, Steven was being overwhelmed by expectations to be like his mother, denying himself an identity of his own. In the past few episodes, Steven's identity has been literally ignored as he is expected to be Pink by the Diamonds. Steven knows who he is but this continuing denial---especially from White Diamond---led to doubt and almost a complete loss of identity. It is nearly impossible to be who you are when everyone around you says you aren't. But Steven perseveres---proves to White Diamond who he really is. This is what ultimately defeats her, having to come to terms with the fact that Pink Diamond is no longer here and in her place is Steven Universe. It is an acceptance of identity by Blue Diamond, Yellow Diamond, and eventually White Diamond which saves their family.
In Change Your Mind, the relationship between Steven and his Pink Diamond gem was made clearer. Steven is basically a hypostatic union. While Steven as a human and his gem can be somewhat separated (though with very disturbing consequences), they are for all intents and purposes a single Steven. The gem is not Pink Diamond (she's gone), but fully Steven. The human part of Steven cannot exist without the Gem part of Steven and vice versa.
The logical consequence of this fact is that a Gem's consciousness or soul can be separated from their gem. Pink Diamond as a person was separated from the Pink Diamond. Where does Pink's consciousness go? Steven is shown to somehow retain some of Pink's memories, therefore she couldn't have been completely overwritten.
My theory, similar to regeneration in Doctor Who, is that parts of Pink's self was rearranged/augmented to form Steven. This process would have left some fragments of the previous person behind, which is possibly why Steven inherited some memories and gem powers. The obvious notable difference here is that Steven is a completely different person and not simply a second incarnation of Pink Diamond.
Ultimately, it's up to the writers to decide how things work and wether to share that to the audience. But it's still an interesting thing to think about.
This season finale wrapped up all the major plot points so nicely that it could have been the series finale. This leaves viewers to wonder what could possibly happen next. Thinking back to the beginning of the show, the whole concept of the monsters being corrupted gems or the existence of a galactic gem civilization and Great Diamond Authority weren't revealed yet. At that point, the show could have just been a simple monster of the week cartoon and it wouldn't seem unusual. We are basically at square one again, having little knowledge of the future plot besides possible hints. From here, Steven Universe could be anything.
This is likely the best time to be a Steven Universe fan. With so little known before the movie, there's so much potential for really weird and ridiculous theories that couldn't possibly be true (but probably will be). Garnet could be a fusion! Rose might be Pink Diamond! Or Lion might be Rose! Or Lion might be Pink Diamond! Sneeple!
With whatever direction the writers will take, I have no doubt that that they will continue to spread the message of empathy, love, inclusion, and just kindness in general. In a broken world that is in need of so much love, I am most thankful to the Crewniverse for teaching both children and adults how to be kind and loving people. At its core, that is what this show is really about. Like Steven sings at the end of the episode—we do not seek validation or attention, but rather we want to help others change their minds for the better.