Hold your horses...
Some points:
1) There is a known 40k photoshop faker on 4chan (the Steel Legion hoax)
2) The image used in that cover is available from the GW Tyranid codex iTunes store
3) "Iyanden" is not aligned with "The Battle For"
4) We have word of "Battle For Macragge" as the Tyranid based warzone book.
5) A plastic Hierophant? The design studio shies away from just ripping existing FW models in plastic.
6) Title font graphic treatment is different from past Warzone books (look at the Pandorax/Damnos cover below)
Attachment 6589
Attachment 6590
My opinion on this is I think we have a prankster that has a passing knowledge of photoshop out there on 4chan fishing - but luckily he's not a very good digital artist. I've been professionally making and directing digital art for 2 decades now. There are a lot of little subtle things that you expect to see on an authentic piece. This one has none of them.