Looks like the development of Diablo IV is going well and as such Blizzard has released a few updates about what we can expect. A couple things I found interesting is that Blizzard is creating a more co-op friendly Diablo IV user experience. Before if you opened a menu in Diablo III co-op only one person could control their inventory at a time.
If you are playing with a friend on a console you might want to both open your inventories at the same time so they are working on providing a user experience where you can do that. Also, they are allowing controllers to be used on PC and be completely re-mappable, something Diablo III does not allow.

That a ton more is available direct on the blizzard Diablo IV blog link below.

https://news.blizzard.com/en-us/diablo4/23308274/diablo-iv-quarterly-update-february-2020