I don't know about Diablo 3, so this is more of a general answer.
If the content you ask about is, or has been available to the general public (usually through a public beta either through sign-ups, a paygate or even completely free and open for all) in a form that they could play the content, it's on-topic.
If the content has never been available to the public to play, it's off-topic.
Additionally, public early access is something that should be mentioned in the tag wiki to allow reviewers to more easily check the question against that particular close reason.