Hmm just a thought, when choosing allegiance, do you choose order or seraphon, as it seems to me based on the page leaks( please correct if i am wrong) that in order to choose the extra abilities/artefacts that you need to choose order, thus temple guard are not battleline units, or choose seraphon, loose the extras but have guard as battleline units.
The Seraphon are part of Order, so I assume that the choices are not exclusive. For example, I presume, an entirely Seraphon army would be both Seraphon and Order.
...but I have yet to see a page confirming or refuting that. I just want the flippin' book to come out already.
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copy and paste from another thread)
You decide with "Allegiance" your army has.
If you choose "Allegiance Seraphon", all your models must have the keyword "Seraphon", and (at that point) saurus guards are a battleline unit.
if you choose "Allegiance Order", all your models must have the keyword "Order": this means that you can have a mixed army (Seraphon / Stormcast / Duardin), OR even a Seraphon only army. A Seraphon only army that has "Allegiance Order", doesn't have the guards as battleline, BUT will have the goodies of the Allegiance order (aka the Battletraits, the Command Traits and the Artefacts).
Basically: Battletraits, Command Traits and Artefacts are made for the Order-Death-Chaos-Destruction factions.
Seraphon and Stormcast are also armies of Order, Khorne is Chaos, Tomb Kings is Death, Orcs and Goblins is Destruction, and so on.
It all boils down to: what is the prevalent "personality" of my army? Seraphon or Order? Khorne or Chaos? the Race or the Faction?
If you choose the Race, you will have the advantage of strong elite units that can be used as "battleline".
If you choose the Faction, you will have the advantage of free battletraits and artefacts.