This write-up is based on an interview conducted by AusGamers with Game Director Luis Barriga and Art Director John Mueller. The following is IcyVein's summary of the interview.
Interesting points:
It seems the story plans for D4 are quite a bit more expansive than just the main story of the game itself, as we found out in a recent interview with AusGamers. Talking with Game Director Luis Barriga and Art Director John Mueller, AusGamers found out a lot about the story, lore and the way they wanted to present it, especially with the reveal cinematic.
"When we were looking at the early animatics that was always the moment. The last shot was the most important shot. Because it's not just a summoning, it's a summoning of the Queen of Sanctuary." - John Mueller
But the big piece of info from the interview has to be the fact that there's a much grander plan for Diablo 4's re-imagined Sanctuary, with the story in the base game being only the beginning:
"Diablo IV is like the first chapter of a book. We want to tell a big story and we want to tell it, hopefully, for a very long time. Treating this like the first chapter of a book and Lilith as a key character in this story, it feels great knowing that there are still all these other characters that could come back in the future. Or, new characters that we haven’t seen before." - John Mueller
There's also the matter of Diablo himself, and it seems like we're not going to be running into him in the base game, as he may be planned for a later expansion:
"It also changes up the formula. In Reaper of Souls if you go up against Diablo, after playing to max level - it’s a battle that’s almost like a like a minor speed bump. Malthael became the real boss. So, it’s also, what if we don't bring him back right away? And instead, take the time to explore some of these other characters first." - Luis Barriga
Personally I don't mind Diablo himself not being at the forefront of the story, and the fleshing out of new characters and new "big bad guys" refreshing. However, the game is still called "Diablo" and if he isn't doing some sort of shenanigans in the background -- apparent or not -- it wouldn't feel right.
But I like Diablo's story telling more than WoW's in many regards. The more interviews I read about D4 the more The H Y P E builds.