A Switch version will be coming after all.
Dragon Quest 11 was actually the very first game that was ever announced for Nintendo’s upcoming Switch, back when it was still known as the NX. However, since then, due to loads of vague and ambiguous wording in official statements and the like, the exact status of a Switch version for the game was unknown- especially since, when Square Enix showed the game off a few days ago, they focused only on the 3DS and PS4 versions, and not the Switch one.
However, Nintendo have updated their official Japanese website, and it has been officially confirmed that there will be a Nintendo Switch version of Dragon Quest 11, too. What version this will be is unknown- the 3DS and PS4 versions of the game are two entirely different games, and we don’t know whether the Switch version will hew closer to the former or the latter, or be an entirely different version of its own. Given that the Switch is a single screen device, it may be closer to the PS4 version, however.
Dragon Quest 11 is currently slated to launch in 2017 for Nintendo 3DS, Nintendo Switch, and PS4. No western release dates have been announced yet.