I am expecting Super Mario Oddysey 2, just The same Styles as the first part but with improved ideas. Super Mario Oddysey is the best selling 3d Mario Game, so Nintendo Will no risk on diferentes Styles on The sequel
When? The problem I could see with them doing both a Botw2 and a SMO2 for Switch is that they won't have the true next evolution of those two series ready for the early years of Switch 2. So unless the teams are a lot smaller, due to the engineshaving been built for these two games, and they are making next gen Zelda and Mario at the same time, I can't see themselves doing this.