The trailer shown at the expo was in Japanese with English subtitles, so it may be a while before an official release window or release date is announced. Not much else information is yet known, but it has been said that the developers are trying to make sure it releases as quickly as possible.
Yo-Kai Watch 4: We’re Looking Up at the Same Sky released for Nintendo Switch in Japan on June 20, 2019 after several delays. Recently, it was announced that Yo-kai Watch 4 would be receiving a free update with new yo-kai and a new map.
Additionally, paid DLC was also announced, which will include a multiplayer mode, even more yo-kai, and other updates not yet detailed.
Yo-Kai Watch 4 is the first game in the series to be released for Nintendo Switch. The western localization for Yo-Kai Watch 3, which combines all three Japanese versions of the game into one, was released for Nintendo 3DS in Europe on December 7, 2018, and in North America on February 9, 2019.
Yo-Kai Watch 4 will launch on Nintendo Switch in North America and Europe some time in the future.