LOL is more than Piltover. Arcane has only covered a remote peninsula during this time. A lot is going on that has in depth lore rivaling this series. Pantheon alone is worth a season.
Is the arcane linked to the V***? I don't really know LoL lore but a YT comment kinda spoiled some things in that regard.
I think the most obvious part they showed (which very much could be a red herring), was that Mel's mom would seize the opportunity of that power vacuum to potentially take over. She was already interested in hex tech weapons and tried to play Jayce.
I'm not sure about what the arcane would be linked to. I don't know League lore. About Mel's mom, I think her taking power was setup near the end of Season 1, but it's interesting to consider that it might be a red herring. I think Arcane's world and storytelling are nuanced enough that's it's not just going to be a straightfoward Zaun vs Piltover vs Noxus. There's probably going to be a lot more subtlety in the conflicts that the arcane is going to play a part in.