From the lips of a keen eyed reader to your ear, it seems like Riot may have slipped something into the Sejuani Art Spotlight. If you stop around 5:20-5:30 mark, you'll see two projects open in the top bar named "Ranca_Golden_Hour" and "Mack3". While I'm not saying these are definitely spoiled content, it is certainly reminiscent to the few other times we have seen strange names in the Art Spotlights.
While a Google image search for "Ranca_Golden_hour" only brings up heart warming landscapes, one can hope they've stumbled on something secret can't they? It's also worth mentioning that Riot is deleting posts and forum banning Summoner's responsible for reposting or pointing out this content, something we saw a lot of when the Easter Teemo and Skarner pictures were leaked.
Note for the two of you that already emailed me: This is definitely not an official thing. This is shaky information and I reposted it because of the similarities to leaks we have seen before, both in style and in forum response. For all I know these are just two images the artist was pulling colors from or different, non League of Legends related projects that just happened to be open. No one should take this too seriously. I don't know anything else about these names, but I'll update if something crosses my path.