Earlier on Twitter ConcernedApe gave us all an update on how things are progressing. While they said the progress is good and could looking at releasing the update in a month or so, we'll have to wait a little while after that to get things ship-shape for the Switch edition.
Update on Stardew Valley multiplayer: still making good progress on fixing bugs, if all goes well it should be ready in about a month— ConcernedApe (@ConcernedApe) April 10, 2018
I'll be interested to see the response to the multiplayer update once it does hit. Stardew Valley is such a calming, wonderful experience at the best of times that sharing it with another person can either make it better or a little bit worse.
I wouldn't be looking too closely at the four-week mark. When releasing on the Switch SDV announced its launch date a couple of days ahead of time and the developer aims for quality instead of speed. It'll be ready when it's ready, but we're looking forward to it.