Not much is known about the Blizzard

According to the Diablo Wiki, Diablo 2: Salvation would've Diablo IV Gold had an increased focus on multiplayer, with guildhalls that players could work together to improve and upgrade. Diablo 2's playable classes would've grown with the proposed expansion as well, adding two more classes to the mix. 

Ultimately, the decision was made to leave Diablo 2 behind and start work on Diablo 3, though it's unclear if those proposed ideas would've been part of the Diablo 2: Salvation trademark or if that trademark was for a completely different project.

When one considers how successful the original Diablo 2 was, it's somewhat surprising that it took Blizzard so long to release Diablo 3. Blizzard had already developed some content for the planned King in the North expansion for Diablo 3, which was then released to players as free content updates.

However, it's not like Blizzard wasn't working on Diablo 3. As a matter of fact, Blizzard North was working on a version of Diablo 3 for years before that particular studio was closed down and development restarted to become the Diablo 3 that actually hit store shelves.

Not much is known about the Blizzard North version of Diablo 3 in an official capacity, but rumors suggest that the game would've taken place primarily in Heaven. It stands to reason that some of the ideas for Diablo 3 were cheap Diablo 4 Gold retained for the final version of the game as parts of it do indeed to take place in Heaven.