I think Captain Toad is ideally suited to NST, as is Mario vs Donkey Kong. I'd love to see them develop a new episode of both series on their own. There's a balance to be struck between constantly settling for remakes or fantasising about unrealistic things. I can imagine NST releasing Toad 2 on Nintendo's next console. Sales aren't phenomenal, but neither is the scale of this kind of project.
What's also very interesting is that, with the release of Peach Showtime, absolutely every character from the Marioverse now has their own spin-off on Switch, with the notable exception of Bowser. I can't imagine that Nintendo, in its strategy of expanding its intellectual property, isn't already thinking about this idea. The trick is to come up with a relevant gameplay idea.