Very happy to see Dark Souls will be shareable.
It could possibly be an oversight.
Game is GFWL, after all, the precedent set by every other game with that specific DRM is not to include it with the family share plan.
it's not the developers, it's the publishers, maybe in the future this will become the indie sharing family plan, as if we don't get drm-free version already.
I forsee a future where every game will be tied to an online account like the rockstar social club.
If you look at the list, its really only two publishers with backwards and broken policies causing the issue.
Rockstar and Ubisoft.
Both Warner, Namco, and Capcom dropped GFWL completely from their future releases.
In fact there is evidence that GFWL is getting patched out from Batman:AA, AC, and Dark Souls. Street Fighter IV confirmed GFWL removal from the next iteration.