At E3 last year, Nintendo had an extensive demo of the game to show off, which you can see below. It takes us through a charming, cardboard-diorama world full of bright colors and a highly interactable environment that begs to be toyed with, knocked over, and explored.
Originally the game was slated to have a 2018 release, and while the year's not over yet, the fact that there was no mention of the game at the Nintendo Direct portion of E3 suggests that we won't be seeing Yoshi's cardboard antics for some time yet.
There's some evidence to suggest this might be the case too, as Nintendo Life noticed that Nintendo's UK site now lists the game as launching in 2019 - though other pages in the site still list it as launching in 2018.
That said, there's another Nintendo-related product that's already made out of cardboard - the Labo. It's pure and fantastical speculation, but it also seems like a game that takes place in a world of cardboard would be a great partner for a product that's actually made out of cardboard.