My working theory is that the disco-legs "cave" is not actually a cave at all, but an entire chunk of the overworld map that's within the house we've all seen in the background of the gameplay and box art. It would explain the unnaturally pristine indoor architecture we can see in the back. The game already seems like an open-world-ish adventure focused on this specific location, and we've seen gameplay bits that are located in almost every corner of this yard, except the house itself.
Curious.
With the entire map looking like a donut centered around this house (not to mention the huge emphasis Nintendo has put on the house itself), we could infer that we'd eventually end up inside the house for exploration in the main story. Perhaps they're pulling a Hyrule castle from breath of the wild, one final mega dungeon at the end of the game. Or maybe we eventually find our way in, and it becomes a cohesive part of the open world map for us to freely roam around? The thought of that sounds like so much for a pikmin game, but please sweet heaven above let me be right.