You know, for how simplistic Spirits are in terms of development, I kinda wish they had a “no stone left unturned” mentality in terms of which properties get representation via Spirits. Not just among Nintendo properties, but among the properties owned by, at the very least, the 3rd party companies whose characters are in base SSBU.
One track I'd love to have seen is Sapporo Slalom, a winter-themed track that could take inspiration from the annual Ice Festival there.