In the old days, New Popstar Ahri would've been a chroma
Chromas are supposed to be variations of existing skins. For example, Pug'Maw has chromas for other breeds, like a Rottweiler (more like Dog'Maw). This was intended to prevent full-priced skins like "green Taric," "red Taric," "pink Taric," "green Xerath," "red Xerath," and so on. Those type of skins don't have appreciably different aesthetics and themes, so they've been released as low-priced chromas for a while now.
And now we have two Popstar Ahri skins. Why not two Dragon Trainer Tristana skins? Maybe there'll be a new sequel to "How to Train Your Dragon" and the studio will make a deal with Riot for a new skin that showcases the new dragon. Or how about a new Arcade Sona skin with a different arcade instrument, or a new hairstyle?
In the same way that Hollywood likes to produce the same movie over and over again (I liked Eric Bana Hulk and Tobey Maguire Spider-Man), Riot now has an excuse to reboot skins. Why come up with risky new ideas when you can just tweak an old idea, tried and true, and re-release it at full price?