Even though this year Orianna has not been the most popular champion, she has always been relevant in pro and normal play. Along with being so important to pro play, there is literally no other mid lane champs that have Victorious skins which I think makes it more fitting. I saw some stuff saying with Swain and Galio should receive them, but honestly they don't have the impact Orianna has; especially with their reworks, and not being strictly mid lane champs.
Edit: Also, to all he people being like "Ugh there goes my motivation to reach gold" or "Demoting to silver now, this sucks," can yall sit tf down? Just because it isn't for a champion you play, or for your role, it doesn't mean you gotta be all negative. I know some of it is joking but most people are just saying stuff to negative and it's annoying.