No split screen.
Its becoming rare with open world games as maps get bigger and bigger. I think given the size of the maps, the console cant handle processing 2 players going to opposite ends of the map at once. Thats why in GTA: San Andreas you had coop for the first time, but it forced both players to stay within a certain distance of each other.
Id be okay with that too (staying near each other). I bet borderlands 3 will pull it off. Borderlands 2 you can cross the entire map without your buddy but if you go through a door to another land, it teleports you both.
I know a lot of it is graphic limitations but it sucks. It seems developers forgot what it was like to sit on the couch with a friend and play video games. A lot of games that make perfect sense for split screen dont even bother making it.