I have been reading the story section of the Tamurkhan book recently. Yes, it has taken me nearly four years. I had read the rules and all the Chaos Dwarf background stuff, I just hadn't read the main story.
It's actually quite a good read, albeit a touch overwritten, with some of it trying a bit too hard to sound epic. But it does a good job of presenting a series of battles, across a variety of locations clearly and without getting too repetitive.
The story describes Tamurkhan and his armies journey across the Warhammer World, starting in the Northern Chaos wastes, before travelling South through the Ogre Kingdoms, west across the Dark Lands, into the Border Princes and then attacking the Empire from the South. In the course of the story, the Chaos Horde fights a variety of foes, including a few quite unconventional armies, such as a tribe of Mutant Savage Orcs living close the Chaos Wastes and an army of Ghouls and giant worms, lead by a Dragon that they worship as a God.
It's a welcome reminder that not every army in the Warhammer World fitted into the narrow confines of the published army books. When Warhammer 3rd edition was published, these sharp restrictions between armies did not exist. The points system was written as a tool box, allowing you to build your own custom troop types and then combine them to produce extremely varied armies. If you wanted your humans to hire Ogre mercenaries you could. If your dwarfs formed an unlikely alliance with a tribe of Giants, no problem. Want to field a Chaos horde allied with the undead followers of an ambitious Necromancer, go ahead.
All of this started to die out with the publication of the original Warhammer Armies book. Although the book was intended to provide strict army lists for tournament and competitive games, in practice everyone started following its rules. When fourth edition was published, the practice started of publishing individual army books for each army, and the divisions between them became crystallised. By the end of eighth edition, virtually every model was part of a specific army and could be used in that army alone.
In fact, this has become standard practice in most games developed by miniature manufacturers to support a specific range of models. War Machine, Kings of War, Malifaux, Infinity, Bushido and so on, all feature rigidly defined factions with each model being a member of a specific faction (though most also include a range of unaligned models usable by all). This means that each faction has its own aesthetic and play style, but doesn't lend itself to player creativity.
In contrast, rules sets that are not attached to a specific range of miniatures, such as Song of Blades and Heroes, Hordes of the Things or Dragon Rampant, necessarily offer players a great deal of freedom to build their own troop types and army lists from a range of types. When your game does not have its own range of models, it pays to make it work with as many different manufacturers as possible.
But the release of Age of Sigmar may have shifted Warhammer armies back the other way. The latest issue of Warhammer Visions features an alliance of Undead and Elves* which combines Dark Elf and High Elf miniatures and includes Elves mounted on Demi Gryphs. I don't know if their owner has made his own warscrolls for these, but I certainly hope so.
If throwing out the old army books and points values leads to more creative army building, I am very much in favour of it. Sadly, Games Workshop has already released two "Battle Tomes" that are almost army books, even if they feature no points costs. Hopefully, as Age of Sigmar develops, Games Workshop won't reimpose a needless division between armies.
*I don't know what an Aelf is and I don't want to know