Yokai Watch 4 may of got delayed to Spring 2019, but it still seems which is going to have a solid year in 2018 with Let's Go and Smash on the horizon. Great numbers for Super Mario Party, with the legs the series is known for I could see it getting close to 700k lifetime especially with a big holiday boost.
2019 is going to be absolutely insane though for Switch in Japan. We're still a ways out and the line-up is already packed with big upcoming titles; New Super Mario Bros U Deluxe, Tales of Vesperia, Fire Emblem Three Houses, Yokai Watch 4, Daemon X Machina, Yoshi's Crafted World, an onslaught of Final Fantasy titles, Luigi's Mansion 3, Animal Crossing, Pokemon Generation 8 and that's just so far.
If Dragon Quest XI S is announced for 2019 in Japan or anything else for that matter is just going to be overkill.