Kings of War is great, I'll be sticking with it for sure. Age of Sigmar, well, I'm sure it's a good game in it's own way, but it's not Warhammer and it's not a massed combat, ranks and flanks style game so I'm not interested. Plus the models are silly expensive. There's not a lot of activity here, but let's be honest, there's not much more on the AoS section of the board either. The death of Warhammer signalled a significant decrease in the traffic to this site altogether. KoW specific boards, especially the Mantic Forums, are doing really well.
Unlike WHFB, KoW isn't won or lost in the list building phase. And I tend to find that games which place less emphasis on the list building aspect of their game (I only really have experience with KoW, SAGA and Hail Caesar in the category) tend to have less online presence. I guess there's just less to talk about. Where games with more emphasis on list building (40K, WHFB, X Wing and Armada) can all be won or lost before the game starts, and there's LOTS of discussion around balance, list optimisation, tournament viable list builds, etc.