The impression I get is Nintendo wants to sell the story content for $30 and the other stuff is bonus content that won’t take a lot of resources to create. They’re supposed to make the DLC seem heftier in content. It’s like when you get a free gift for buying a thing at say, Target. That bag or whatever wasn’t really the reason you bought the main item, but it’s yours now so you might as well bring it home.
Without having played Xenoblade Chronicles 2, I can’t comment on either way whether I’d be interested in the DLC. I have the game preordered even though I’ve had some trouble getting hooked in RPGs. If the new story content features is the true final boss or something, I kind of have a problem with that. I’d like the main story to stand on its own rather than end on a cliffhanger and have the final boss and plot resolution locked behind a paywall. If the DLC is merely a side story with its own exclusive boss, I wouldn’t feel like I got nickel and dimed paying full price for an incomplete game.