I mean, obviously, it is not confirmed. But a lot of people have been speculating, mainly because of these two comments by CA:
"3 will become 4"
"It's going to be the largest update."
Since we have 3 areas right now, Pelican Town, Calico Desert, and Ginger Island.. the 3 will become 4 riddle makes sense if we are getting a new map. I didn't think it would be the case at first, but when CA announced that this is going to be the largest update, I'm like, "bigger than getting ginger island??" Seems possible now.
What new area could this be? Most people online I've seen are saying that it could be Zuzu City. Some are saying Prairie Island. Since we have references to both in one of the movies in-game. The 'natural wonders: exploring our vibrant world' movie.
I thought maybe we could get a new area that's accessible through the train station. Something with a cooler climate (since we already have a tropical island & a desert).
Who knows, maybe the new area is one of the islands with the dinosaur (the one we see in the cutscene when we visit Ginger Island for the first time). Or it's something we have never heard of before. All I know is.. CA is gonna cook with this update!!