I had no idea way back when I first saw this picture that the cutie mark was not legitimate intel; your art made me presume that this mysterious "Cadence" character was the new alicorn of Weather, and it sparked a story in my head which I'm very much enjoying working on. I guess what I'm trying to say is, thanks so much for the direction of artistic license you took here. I found it inspiring.
Celestia's sending fanon to the moon again My guess is she's either a relation of Celly and Luna or, she rules a country outside of Equestria... Or , to play the really far-fetched angle, the mane 6 go back in time for some obscure reason
If I were to connect dots, I'd say shining and cadence is blue bloods parents who rule another country. Because Cadence is a alicorn that would make her kin to celestia maybe. It would also solve the blueblood relation mystery.