The new Victorious line theme seems to be more about blue/purple cloth with gold accents.
Sadly, the Fiora looks like she's a throwback to the old line of Victorious... whereas Diana looks like she's more in line with modern standards of Victorious skins. Maybe if Fiora's crown didn't look as jagged or if her armor was White/Blue instead of black.
Also... we're overdue for mid/sup Victorious skins.
However, it's more measured by the amount of impact said champ had on their particular season. Mao had a big impact early S6, Graves had a big impact early S7.
Check the Ask Riot for how they decide on Victorious btw.