Luna from Animal Crossing, a fan favorite character new to New Horizons, was teased in the Summer Update trailer. First introduced in Animal Crossing New Leaf, Luna is a Tapir who operates the Dream Suite in New Leaf. The trailer suggests that while the Dream Suite itself will not be making a reappearance, Luna and Dream Towns will.
The Dream Suite in New Leaf was a means of exploring other players' towns and learning their custom patterns that did not require the other player to be online. Basically a player could enter the Dream Suite, a building next to Club LOL, and upload a copy of their town to the internet, and then in turn visit other peoples'.
Luna Animal Crossing: New Character Teased in New Horizons Summer Update
When visiting towns in the Dream Suite, players could also find Wendell, a Walrus NPC who would give them access to custom patterns the town owner had chosen to upload. Towns could be visited either randomly or by putting in a specific town code. In New Horizons it appears that most of this process has been streamlined so that you can enter dream islands simply by going to bed.
First and foremost, only the visitor actually needs to be online. Second, since a dream island is just a copy of the island made when you decided to upload it, you can show off your island online without fear of vandalism. Players in New Leaf also took the time to create all sorts of crazy themed towns, one of the most famous being the horror themed town, Aika Village.
Additionally since its a static copy, you can build a themed island, upload the copy and then put everything back the way it was and the online copy will remain as long as you don't decide to upload a new one. Players were also previously unable to use shops in Dream Towns or keep items they picked up there but we'll see if that changes in New Horizons.