Theory on Kayle and Morgana: guiding light and punishing darkness
So... Now that my second favourite character has been updated, it's theory time! Without further ado, let's get into it.
##The Sword of Justice
So, Morgana's bio informs us that "great blade wreathed in shadow and starfire fell from the heavens". We can safely assume that both shadow and light were (or rather, are) parts of the Aspect of Justice. The twin sisters each took a piece of the sword, awakening their powers in the process. Kayle inherited the Starfire part, that is to say light, and Morgana inherited the Shadow part.
##The Guiding Light and the Punishing Shadow
Now, light usually is represented as a good thing (good and evil are abstract notions, but hopefully you'll get my point). Light is often the element that guides people through the dark, that reassures people.
Shadow, on the other hand, is usually seen as a bad thing that terrifies people, associated with aguish and this kind of negative feeling. We usually don't know "what lurks in the shadow", as if monsters were waiting to come and devour us.
##The Righteous and the Fallen
Now that we've mentioned that, let's get into the core of the topic. I believe Kayle's light as part of the Aspect of Justice was to guide people into repentance, while Morgana's darkness are supposed to punish the guilty. However, the opposite happened. Kayle is the punisher, while Morgana seeks to help those who are repentant. So they basically swapped the roles they were supposed to have (or at least according to the powers they inherited from the Aspect of Justice).
This is a big stretch because we don't have much on them, but I believe that's possible, and that it could have its importance in the future.