Masahiro Sakurai, who is widely known as the creator of franchises like Kirby and Super Smash Bros., has recently tweeted that yesterday's announcement, during the Nintendo Direct presentation, is indeed a brand-new game and not a port of Super Smash Bros. Wii U/3DS. The tweet is in Japanese but we now have a translation of it thanks to the people over at Siliconera.
According to the translation, Sakurai says that: "Although we're barely at the stage where we've only announced the title, I've been quietly working on it day after day. Please wait until we can reveal its contents, or until the time of its release!!"
While the official release date has not yet been revealed, the teaser assured Super Smash Bros. for the Nintendo Switch is coming out this 2018.