>>20879118
>>20879111
The pirate species itself could fill any of the niches left open by the current 40k. Ones which immediately spring to mind are a reptillian species, a 40k Ogre species, an insect species and an aquatic species. However, old ones, slann and dog soldiers are all reptillian, and so could be argued to fill that gap, even though none are major armies. You could also argue that the Ogryn are the obvious successors of the WFB Ogres in the 40k setting, and even if they weren't, big fat oriental mercenaries doesn't really fit pirates. That leaves insects and aquatic species; a very small minority might say that Tyranids are insects, but I think they're more body-horror-what-the-fuckery rather than true insects.
Man sized, bug eyed, super strong ant and fly people, backed up by slow, humanoid slugs. An insect species would open up all sorts of ideas for natural weaponry, like stings and pincers, and perhaps some interesting ideas for technology.
However, an aquatic species could also be pretty cool, and it seems pretty fitting for pirates, seeing as they rule the seven seas. So, I think I'll expand on this aquatic idea more. It would probably be a good idea to make an aquatic species something more than walking fish, because then they'd just end up looking like tau. I'm thinking something like a bizzare mish-mash of crabs/lobsters and squids/octopuses. Twisted, ridgey exoskeletons protecting flailing tentacles, ending in bizzare limbs which seem to be a mix of suckercups and pincers. Perhaps this aquatic species cannot breathe air, so almost all units are complete with a handful of water tanks and special breathing masks strapped to their person.