Pokemon Stars is reportedly being developed by Game Freak, the same studio behind Pokemon Sun and Pokemon Moon. According to Eurogamer, the February reveal teaser for the two games features a split-second shot of the HD in-game model of new bird Pokemon Pikipek, which is apparently for the Switch edition.
This parallel development structure has allowed the Switch edition to already feature working versions of Pokemon Sun and Pokemon Moon content. However, work on the Switch edition was reportedly paused a couple of months ago to polish the 3DS versions for release, but will now resume with the development of features not found in those versions.
The Switch version will reportedly feature the same map, routes, cities, and art style of the 3DS versions, though with separate, higher-resolution assets.
According to Eurogamer, the Switch version was initially planned for release in summer 2017, but has since been pushed back to later in the year.