First up is the cover page. Battletome: Tyranids has the same name as its corresponding codex, but as I move into some of the more esoteric keyword arrangements, things will get a bit divergent. For example, Space Marines will be Battletome: Imperium Astartes, and Tau will be Battletome: Greater Good (I've been doing some fiddling with Tau keywords, namely putting Greater Good on everything and getting rid of the Fire Caste keyword.
The other notable thing here is that I'm doing all the art myself, so I know it's not going to blow anybody's mind, but I felt that the pages looked too naked without it.
Each "Battletome" will have an intro page explaining (very briefly) what the heck is going on and why there are 40k armies in Age of Sigmar. The "artwork" on this page is actually just public domain space photography run through a paintbrush filter in microsoft office.
The new rules content in the "Battletome" will be Allegiance Abilities, including Battle Traits, Command Traits, Artefacts, and a unique Psychic Discipline when appropriate. You may have already seen the Tyranid Battle Trait (although it's still a work in progress), but here it is with my home-made illuminations.
I've been working on this for all of the armies (including Dark Eldar and Necrons!), so it's not just Tyranids. That is just a taste of things to come.