By now, I know that many readers will have already seen the Horus Heresy "formation" that has been published on to the Facebook group of Games Workshop Halle (Germany).
There is some excitement over this as, if it proves to be true, represents a number of interesting developments for the Horus Heresy. Firstly, and most obviously, it shows that 30k is going down the 40k route. I'm a little uneasy about this personally, as I think that the way that Forge World are pulling off 30k is fine as it is and does not require formations to spice it up. Indeed, being a very old timer, I remember that formations were originally introduced via Apocalypse. From there, they appear to have leaked directly in to mainstream 40k. I don't actually like a number of the formations in the current meta-game for 40k as I think they're a bit broken (too many freebies for too little effort -- particularly in certain space marine demi companies, for instance). I much prefer the formation-free approach (the "classic" approach) that 30k has taken with basic army lists and everything priced very fairly. This move seems to be GW encroaching on territory.
It also is suggestive that this might be part of a bigger 30k publication of formations that might be coming out soon. Or perhaps part of a campaign.
Alternatively, it could simply be just an in-store campaign.
The one thing that strikes me is some of the discrepant language used in the publication.
Not only are they using "Praetor" (a 30k term), but they are using 40k specifics as well.
Read down to the bottom of the image and they use the term "Chapter" (usually associated with 40k, but some evidence of that in 30k as well).
The artwork is very 40k, having been used numerous times in the past.
The headings and margin artwork is highly 40k.
So what is going on here?
I'm going to say "in house rules" for a GW campaign. Happy to be proven wrong as always though! I wouldn't mind a full publication based on 30k. But I want FW to publish it, not GW. But I'm biased :)