While it's taking a bit longer than we might have hoped, Stardew Valley is very much on track for its release on Nintendo Switch. After being announced six months ago, developer Checklefish took to their official blog to offer updates on not only Stardew Valley but Starbound, Pocket Rumble and current events within the studio. As it turns out, the team has moved into a new office recently, which might explain the relative silence surrounding the Switch port, as they are a pretty small team, but they did offer up the insight that everything is going just fine.
Here's the most relevant snippet:
"I know you’re all waiting for Stardew Valley on the Switch! I see your tweets! The port is in testing now, and we’ll let you know as soon as we can confidently announce a release date. We generally don’t announce release dates until quite close to launch, when we are at least 95% certain that nothing will go terribly terribly wrong."
They also mentioned that the game's upcoming multiplayer mode is still in the works as well and that they're hoping to do a beta test for Steam players sometime at the end of 2017, with an "early 2018" release on Windows, Mac, and Linux and sometime later on consoles.
All in all, Stardew Valley is doing very well behind the scenes, and it's just a matter of time before we see it in action on Nintendo Switch.
[Source]