Being part of the top management, I can provide replies.
Rules: the 2nd edition is very stable, it has been released in December 2018, and won't change in the foreseeable future (you can count safely on 5 years).
The yearly adjustments affect the Arcane Compendium, which complements the rules with the spells and magic objects, and the 16 Army Books. For the most, it consists in small points adjustments.
Fluff:
Although lots of snippets have been released in the magazine The 9th Scroll (that's kind of like White Dwarf in the '90s), the Background Compendium is still waited for. More effort is made for the armies as they are redone.
Armies:
Army Books are being overhauled and get a full fluff treatment in the process.
Currently, Sylvan Elves, Undying Dynasties (both will be redone at some stage), Daemon Legions and Warriors of the ark Gods have their detailed fluff - DL benefiting from a fluff supplement.
Infernal Dwarves are in beta stage and got their fluff supplement too (this will be done for all factions fro now on).
Dread Elves are in the works and get lots of spoilers discussed with the community, to test the reaction.
Vermin Swarms just started.
The next in line is Kingdom of Equitaine.
No indication that Empire of Sonnstahl would be dealt with any soon, the current version seems to work fine.
Besides, there are numbers of supplements: Asklanders (Norse WDG), Makhar (steppe WDG cavalry), Cultists (DL worshippers). The standard seems to be that each army gets two supplements after being redone.
Additionally, there is a Giant Supplement, allowing each faction to get their giant, plus advanced magic, scenario supplement etc.
Other News:
Two supplement games already Pirate's Peril (simplified game), and Games of Zagjan (hilarious Orc-lympics Games).
The simplified introductory game Quick Starter is being currently redone as Essence of War.
