The Wood Elf Army Book discusses their view on the nature of the Lady of the Lake (and Ariel). Each is a focus of their land and have their specific domains. Supposedly, these foci are the key to beating back Chaos. The High Elves consider the Everqueen the embodiment of their land.

The Empire has Sigmar, with Middenheim as his holy city. Periodically, Chaos attacks the Empire with the desire to carve a path of destruction and possibly destroy Middenheim.

GW has always used the invasion of Chaos as the focus of their timeline. The Storm of Chaos from a few years back kind of fizzled. I suspect many upcoming books will have more about Chaos attempting to capture/destroy/pervert these foci. The invasion of the Empire by Archaeon might be cast as destroying the focus of Sigmar's Faith at Middenheim. Skavenblight might be the corruption of one focus through the use of Warpstone, giving rise to the Skaven.

This tells us very little (if anything) about mechanics. However, I think this suggests the direction of upcoming storlines (background).