While the Diablo team at Blizzard has now settled into working from home, they've released another quarterly update today on the current state of development. They'll be focusing particularly on multiplayer and the open-world environment.
The developers state that for the latest milestone, they focused on roughly fleshing out all the elements of a region called the Dry Steppe – including campaign content, open-world elements, items, a PVP area, dungeons, and a cutscene to conclude the narrative within this region.
About the open world
"One of the most important new features for the Diablo series is the open world of Sanctuary. So while you can focus on the campaign and work your way through the story, there are also a variety of open-world systems and content to discover on your journey. If you want to take a break from the campaign to explore the world, craft items, or try your hand at PvP, you can do that."
About the multiplayer
“Finding the right path for multiplayer gameplay in Diablo IV was quite a challenge. Our goal was always to incorporate elements from shared game worlds without making it feel too much like an MMO. This is, of course, more a question of philosophy than purely technical possibilities. In our opinion, the game feels less like Diablo and the world seems less dangerous if you encounter other players too frequently or in too large numbers.”
You can find the complete and comprehensive article on Diablo IV here with this link.