I think all the army specific forums have taken a hit, some are just shells now. Chamber of the Everchosen is lucky to get a couple threads active each month in their subforums and the Wood elf forum was going to shut down though it's now going to be relocated the high or dark elf servers.
I started with 8th and with Tomb Kings when they got their current book. I also started frequenting the Tomb Kings forum. That place was always buzzing! Even though the relative weakness of the army was evident quite soon after the other 8th edition books started coming out, the active forumites clearly enjoyed being the underdog. I got so fed up with transporting those models and the rumours of Tomb Kings and Vampires coming back together that I decided to sell my army. Slowly I also stopped visiting the forum. Few months after AoS came, I checked it out and noticed it was still somewhat busy, but many of the active members were gone.
The Tomb Kings forum is still the busiest I have seen, even more than LO at it's peak. Still, this is the forum I have enjoyed the most, and it has always felt really active. Especially after I joined the Necrons forum, a bit before the new book came. That forum felt so empty. Even when they got a new book, it never got even close to the regular traffic of Lustria Online. It felt weird, because I had heard that 40k was much more popular than Fantasy Battle, so I expected their forums to be more active as well. Wrong. Then I started Chaos Daemons, and though since they can be played in both 40k and Fantasy Battle/AoS, they must have a super active forum. If they do, I still haven't found one. The Daemonic Legions gets maybe one post a week, if even that. Funnily, though, their Fantasy side of the forum is much more active than the 40k side.
I have been somewhat inactive lately, and that is a combination of several things. I have been painting Necrons and, to a lesser extent, Daemons. I have been busy with work and trying to sell my childhood home. I have always been more of a painter than a strategist (half of the time I can't even pronounce that word!), so while in 8th I could give some tactical advices, I'm not very familiar with AoS and 9th Age (waiting for my friends to catch up with that so we can have a game), and that limits my activity on the non-painting related areas of this forum.
Wow, so many words and haven't practically said anything of substance! Umm, I guess the TL;DR version is that, while it's been quiet here lately, we are still a very active forum, with lots of appeal to many facets of the hobby, and I firmly believe that we will stay that way for a long time.
Unless
@spawning of Bob leaves the forum, then it's all over.