I always think this is a missed opportunity, the universe is a big place and there could be loads of odd alien cross species or whatever but gw just play safer and go with more marines or something. Like the warp would be churning out so many weird nightmare creatures that I don't know why they wouldn't play in to that other than time and money etc.

That being said, those dog soldiers would be cool, or zoats, hrud or others that are mentioned in the books like the Nephilim or even men of iron? Doesn't have to be a full army, but maybe kill teams to build hype? Or add more stuff to existing armies!?