No word on what characters to expect or the other kind of content the update will bring, but we don't have to wait too long to find out!
Calling it now, Gold Mario and Pink Gold Peach. Maybe a Mercedes-Benz if we're lucky. :p
Rosalina sounds likely. Daisy, Wario, and Waluigi would be a pipe dream, but if Toadette has managed to sneak her way into main series Mario, I suppose anything's possible.
Yessss, I'm glad to see that more significant content is coming to this game. Really hoping there are new stages or at least new interactive elements in the Kingdom Builder.