DLC for first party Switch games has been virtually all about expansion passes. A single significant one-time payment ($20, $25 or $30 depending on the game) gets you a notable amount of additional content, individual content purchases are impossible. The only outliers, that I can think of right now, have been Mario+Rabbids and Fire Emblem Warriors, both of which had a season pass as well as the option to buy individual DLC pieces. Another outlier is Super Smash Bros. Ultimate where the popularity of the game has caused the introduction of a second fighters pass, but the new fighters still have to be purchased as a package as individual purchases are not possible.
In light of Nintendo's quite consistent DLC strategy for Switch, it would already be surprising if Animal Crossing received multiple smaller DLC packs that go for $5-10 each. EA-type stuff can be safely ruled out. But you should expect an expansion pass that costs $20-30 because a lot of Nintendo's popular Switch games have got one. More often than not, the content of the expansion passes has justified their respective price, so if we go by track record, Animal Crossing should be fine with and without an expansion pass.
Yea I suppose you are right. Least Nintendo treats DLC like companies used to with computer game expansion packs. There is actually enough content in pack to warrant purchase.