I think the current lineup hits all of the major beats. A Yoshi's Island subland could work fine with rides for really little kids, but I also think Yoshi's Adventure represents that sub-franchise fine as well. I don't think any other Mario Spinoff series is anywhere near popular, relevant, or condusive enough to make a full expansion out of. If we end up with SMB+DKC+Mansion with a Mario Kart and Yoshi ride within those lands, that already feels incredibly well-rounded to me. No Wario Land or Paper Mario needed, they just wouldn't move the needle.
I think we'd need to see Galaxy 3 before a theme park land or ride is added. Galaxy was sold on Switch for less than a year, and Galaxy 2 wasn't brought back at all. Those games also released 15 to 20 years ago now. I think it's more likely the SMB subland stays as is for a good while.