When they first announced the Legion Shadow rework, they did it for no other reason than simply “because” as Shadow worked and played just fine… great even in WoD.
But they wanted to make the changes in Legion to fit with the weapon artifact system and instead of Shadow remaining mysterious and up for interpretation, they attached this whole void/insanity/old god tentacle theme to it.
In doing these alterations, they completely tossed shadow upside down in changing our resource system to Insanity instead of Shadow Orbs and made it drain by default alongside removing a lot of spells we had access to in WoD both rotationally and utility while introducing every other spell or mechanic centered solely around maintaining your insanity drain which overtime caused any talent that didn’t affect your insanity drain to become a worthless talent since it was the core mechanic that held everything in shadow together.
This insanity drain mechanic become a source of design restraint as they have now designed the entire spec into a corner of insanity maintenance. This is why stupid things like casting Dispel Magic eventually granted insanity because every GCD you spent that did not grant you insanity caused your entire damage to plummet.
That means in any high movement or fast paced gameplay where you are out of combat for any amount of time like between pulls in M+ or PvP or heck just doing world content, you had to ramp up your insanity which caused you to be extremely weak and vulnerable before you get enough insanity to put you into Voidform for which in areas like PvP or 5 mans means you are pretty worthless if you can’t get a cast off while in Voidform due to either movement or interruption which causes you to enter a negative feedback loop on insanity generation which just forces you to spend more time playing like you are short of breath as if your held under water.
It was I believe shortly after the launch of Legion that the dev who imo butchered Shadow left the company for whatever reason and the spec has been limping along ever since.
It was a constant struggle to get Voidform under control and into a state that walks the line between overpowered and negligible between all the patches throughout Legion and BFA through multiple tuning passes and slight changes but nothing in the form of major reworks.
It was then in Shadowlands alpha that after loosing Legions Artifacts and legendaries and BFA Azerite armor and artifact necklace essences that Shadow was in a poor shape and near the end of the development cycle did shadow finally get a mini rework with Voidform no longer having the insanity drain mechanic and the inclusion of Devouring Plague returning as your resource consumer as well as a handful of talents that interact with Shadow instead of solely insanity resource.
But then the developer that was working on that left after that announcement of changes.
Then in the DF alpha, the dev that was in charge of Druid and Priest left early into the process and we were left with nothing till the last month or so with very little time to test and provide feedback and in turn get updated iterations on the launch of DF talents for Shadow.
Then in 10.1 we got a revised or I guess “completed” Shadow tree with the caveat that more work is needed and to come but they don’t have anymore time.
Then 2 years later we are at this point in the events of no communication and seemingly no vision as to if or when we will see further updates.
It’s been a long rough road since the end of WoD for which I would argue over silly reasons leading to many dead end paths.
Hope to see some better progress in the future but I won’t be surprised if we don’t at this point.