No idea, but here's another curiosity. The url for each dlc is as such. The Ashes dlc url is ashes-urok, the Embers of Rage dlc is orcs, and the third dlc he has named "Broken World" which routes to an error page is marked as spydre. A spider campaign or something of the like? Curious.

edit: Another thing to note is that in the game statistics page at the very bottom there are two campaigns listed as "spydre" and "Spydrë"

edit2: I just now noticed that rexorcorum also has that dlc listed.

edit3: On further search using the wayback machine I have confirmed a couple things. First is that the Broken World dlc is recent. It appeared last year sometime ahead of March 19, 2016. Second is that the "spydre" campaign has at least been tested as far back provably as July 28, 2011 alongside other campaigns such as the "orcs" campaign which we now know as the Embers of Rage campaign, and a yet to be seen "undead" campaign. That means that this is likely something of a teaser or a hint at what's to come. Whatever our Great Lord Dark God has planned he is at least confident enough to list it in his currently owned dlc which can be publicly viewed, even though the dlc page itself is inaccessable.

It appears Broken World won't be the only mysterious dlc to pop up, because now there's also forbidden cults. Looking forward to seeing what the dlc is like when it's announced officially.

Has anyone else gotten this message upon entering Angolwen? http://images.akamai.steamusercontent.com/ugc/85971431429836056/87316CF3780C3EB1B23ACD75286B6D0EA445B6E9/

Hey guys, i don't know if you have read this http://www.frame-rate.com/2017/02/24/death-hands-darkgod-tome-4-breathes-life-roguelikes/
In this interview Dark God more or less announced the upcoming DLCs Broken World and Forbidden Cults.