First off, Daxxarri has shared a summary version of every single boss's lore with us. If you're wondering just why exactly you're fighting a triceratops, this blog will tell you! It's really interesting to learn the lore behind the bosses, making the raid more than just a series of puzzles. The stories revolve around power and its destructive effects, from Jin'rokh, who started life as a quest-giver in Zul'Gurub, before being corrupted by the Thunder King and given shamanistic powers, controlling lightning alongside his huge strength to crush his foes. Horridon is a sadder tale, for me, as he seems to have simply been captured by Jalak, and forced into battle. Having fought him, though, he doesn't seem very peaceable.
There are several other great stories in the blog, for example, did you realise that the Mogu actually created the Saurok? I sure didn't. The stories, in brief, are very similar to those in the dungeon journal, along with the recent addition of Ra-den, who, it is revealed, was guarding the Engine of Nalak'sha.
But more than that, there is what could almost be considered a director's commentary, provided by Lead Encounter Designer Ion Hazzikostas. Ion provides a brief summary of the team's approach for every fight, how they came into being, what was the inspiration behind them, and so on.