First, some background primer. The production pipeline for video games normally has these phases (simplified since the actual process is obviously much more complex than this):
#1) Conceptual: the ideas of what the game and game play could be like.
#2) Pre-production: where you have producers, designers, engineers, writers, graphic artists, and programmers working on a general design document which covers things like the story line, game play mechanics/rulesets and objectives, character/world/level designs, technical specifications of the target platforms, etc. The story is what normally drives the other parts of the design and design prototypes are created to flesh out those ideas and concepts. The UI (menus, game controls, etc) are also described in this document.
#3) Production: when the pre-production ideas and concepts have been finalized, development transitions to the actual production phase. This is where more producers, game designers (including those tasked with level and quest designs), graphics artists (modelers, animators, visual effects, etc), and actual coders are brought into the project.
#4) Post-production: all production work has been completed and features of the game are typically frozen at this point and also considered feature complete. Actual quality assurance game testing begins internally (alpha test) in order to uncover the most egregious issues which are then addressed by the respective production teams. Some companies also go with limited technical tests that include outsiders (i.e. free testers). Other companies/publishers have also used these testing phases as part of their marketing/PR push (including monetization with packs that guarantee access to closed alpha/beta tests) instead of actual testing. Beta test code normally follows where there is more granular play testing internally and nowadays, by inviting the actual player base to go at it.
As is the case with most software development, issues are categorized into differing priorities; the highest level ones are dealt with first while the lower level ones are allowed to slide into the known issues list with the beta test code. There’s an eventual point where once key milestones are met, that code goes into a final/release candidate (aka golden master) state that allows it go into actual manufacturing (for physical or even online distribution). Logistical lead times for actual physical product (manufacturing and then distribution to retail point of presence) are as expected, very time sensitive meaning that the code normally won’t be bug-free at launch. Lower priority issues will normally be dealt with in a post-release patch (where there is already a team working on it).
So with this brief primer out of the way, Blizzard’s job listings for the unnannounced Diablo project (as of February 8, 2019) offers some insights as to where the company is with this project. The majority of them are for positions that tend to be part of the production phase (art and animation designers, audio engineering, technical for rigging and visual effects, additional producers for this particular phase of the project).
There are of course other areas that don’t require actual hiring for this project (this includes modelers since Blizzard has a team already in place as well as cinematics which that team has probably been working on for this project based on what has been finalized in phase 2. I had previously guestimated this work was being done in 2018 in order to do a teaser (which never materialized) for the 2nd half of the year. Given the lead times for other cinematics (Legacy of the Void’s cinematic took them an year to complete), that team has their work cut out for them even if the first peek is slated for this years BlizzCon.
I would say the project is at least an year behind its initial target dates (as I still believe they had intentions several months in advance, to at least announce the title in the second half of 2018 with the latest date being by BlizzCon 2018; and we all know what happened instead).
