Game Workshop wouldn't even think about passing the idea. It wouldn't get near verification for them. Never happen. Closest you'll get is SoB.
As previously stated multiple times, there aren't any females in the Space Marines in lore so Eternal Crusade won't even go there. And rightly so! The only way to include female combatants would be Adeptus Sororitas , The Sisters of Battle, female warriors from the Imperial Guard, or those of the Inquisition.
Yes there are male Eldar, they are in every aspect, including Banshees, although it's a very small portion. But these are the SM subforum, keep the dirty Xenos talk out of here.
I have no problem with female players or characters in 40k... but the game was made 20 years ago when female gamers was unheard of. Now... i'm really glad they have the Adepta Sororitas not to mention female Eldar & Dark Eldar, Guard, Inquisitors, and so on... but the lore says both that the gene seed will not work with the female body and since the space marines are a WARRIOR MONK order... the whole, no mixed sexes in religious monk orders thing kinda puts the last nail in the figurative coffin.
SOB in the game would be awesome for me but there are so few female players that are into 40K. I played Space Marine on 360 and PS3 and there were only a handful of us girl gamers who got into the game on both platforms. Although I do know a ton of guys who like making girls characters in games. I will just be making my Space Marine armor look Fabulous. PRINCESS SPACE MARINE!
Imperial Guard and Adeptus Sororitas (Space Nuns) are there as female alternatives, Regular people or Amazonian Stronk Woman - the options are there. But Space Marines, ARE ALL ABOUT HE-MAN/Action Man!