Super Mario Galaxy was released in November 2007. Roughly 18 months later, at E3 2009, Nintendo revealed Super Mario Galaxy 2.
Super Mario Odyssey was released at the end of October 2017. The game was a massive success, and is prime material for a sequel that builds on the mechanics of the first game and that offers plenty of new worlds. I think it would be great if Nintendo made a sequel, and announced it at this E3 2019.
When I was playing Odyssey, I had that same feeling as when I was playing the first Galaxy: that the game felt like it could have easily had had more content, content which could form its own sequel. I think it would be a waste if Nintendo didn't go back to Odyssey. Odyssey 2 could also take a page out of Galaxy 2 by offering players more difficult challenges than its predecessor.
In any case, I really want an Odyssey 2.