Though Ubisoft has announced a host of new entries in some of its major franchises, the studio isn't opposed to revisiting others, like Splinter Cell and Prince of Persia, that haven't been seen in several years.
Nintendo carefully considers a lot of factors before it makes an announcement. While some major products like the Switch itself have a short turnaround between reveal and release, others like the recently-unveiled Metroid Prime 4 make sense to announce earlier in the development cycle.
Nintendo revealed the game during its Treehouse Live event today at E3 2017 and relayed the news on Twitter. The title is a remake of the original Mario & Luigi: Superstar Saga and features a new mode called Minion Quest.
Nintendo dropped some teasers during their E3 Nintendo Spotlight. A very brief teaser was shown with Metroid Prime 4 logo. During the Nintendo Spotlight at E3 today, The Pokemon Company revealed that a core RPG Pokemon game is in development for Nintendo Switch.