It's honestly baffling how many people call foul with Inklings being "too new."
Like, say Brawl had DLC. Say in 2010 they added Zip from FlingSmash. Ever heard of him or his game? Of course not. He was a complete dud from a critically panned Wii title. Splatoon, on the other hand, already has the kind of staying power to be considered an A-Lister for Nintendo. Praised and acclaimed critically and commercially, by both the casual and hardcore crowds, and in both the East and the West.
Splatoon is not FlingSmash. "Too new" is not an issue. They already have the credentials.