I'm not sure Blizzard is in the position to make anything that is going to be worthy of the Diablo brand these days. They're lodged under the thumb of Activision, so, what would we be looking at as almost certain?
- Creating a campaign that will follow up one so bad that it was basically patched out of the game (effectively) by Adventure mode in Diablo 3: Reaper of Souls. Oh, and, under a regime that has started removing campaign modes from their games. A real recipe for quality.
- Grotesque horror themes are going to push away some users - it should have a more accessible feel to ensure maximum purchasing audience. Definitely going to soften the tone further.
- They're not going to want to retcon the entire plot from 3, so, we have to continue from the mess that is now the Diablo story universe, unless it's a prequel. And, yes, I know I already mentioned plot. It was that bad. In an ARPG it shouldn't even matter - it was so bad in Diablo 3 that it matters twice.
- Activision isn't going to want them taking risks - who cares if the genre has seen notable improvements and refinements from the likes of PoE, Grim Dawn, etc... we're looking at more of the same formula, likely simplified further. Diablo 3 was already pretty heavy handed in cuts from D2, could you imagine a cut back Diablo 3 system?
- While we'll almost certainly not see full Activision greed, Blizzard has shown that they're not above selling anything without a stat-point attached these days. Expect more micro-transactions than you can swing a Loot Box at if you want to look cool - and a full retail price to go along with them. Maybe sell us some character slots while they're at it.
- It can't be marketed as an E-sport, so, expect minimal after the sale content/support.
- ...Unless they make it a true live service (Which could fit why they are not ruling out hiring a Lead Character Artist and Lead Concept Artist for a game which is not even ruling out a 2020 launch). If it fails like D3 did at first? Go ask the Anthem player-base how that feels.
I loved the Diablo franchise, but, at this point the horse is dead. If you really want to come out and bludgeon it a few more times, just don't expect us to show up to watch.