The Atlas site has been updated with a preview of Mega Update 3. There are no definitive plans for release, but devs are providing players a peek at new content. When the update launches, it will come with an array of new islands and Discoveries, new sail skins, the new Sea Horse creature, and the ISO: Blackwood standalone map. Lastly, a single player mode is in the works that will not require running a server in the background.
Single player mode will have all current content available "that includes the same massive world with each and every island". Devs are working hard to get it onto the beta branch sometime in mid-July.
Check out the full update preview on the Atlas site.