I think we’ve been in the past for a good three books, and between The Promise comics and what I increasingly think will be an episode almost entirely of flashbacks somewhere in this season of Korra.
But I don’t think this series will go “full Digimon.” One of the best things about how Korra has evolved thus far is it’s greatly based on the rules established in A:TLA. It’s a natural extension of the world, and even if Big Daddy looking mechs are a little jarring, I don’t think they’re more of a stretch than something like The Drill from 70 years before.
I trust the world-building, and if A:TLA was ancient and this is industrialized, I’d love to see what “Modern” is in this world. But maybe there’s no place for The Avatar in modernity.