So it looks like we have a clear idea of what's to come with Decadence and Death, leaving (Da Best) for last, Destruction. I imagine we are still awhile away from seeing what it will be but the mystery April warband definitely seems like something to look forward to.
I have a few speculative ideas of what it could be (in no particular order)
1. Bonesplitterz, would make sense as the logo has a bone look to it, and it would be the first new non ironjaw orruk for AoS and would fit the hunter theme of Direchasm.
2. Spiderfang, would be awesome but not much about the logo screams spider to me, plus it would be the 3rd warband for both Grots and gloomspite.
3. Silent People the one I'm most excited for. Points in favour would be the similarity of the icon to the mask of the silent people and their amber bone equipment, as well as them being teased throughout this Beastgrave and Direchasm. The biggest point against them however is that the katophrane were also teased that way in the first 2 seasons.
Whatever it ends up being though, it will probably be something interesting.