Honestly, I don't know why they don't allow you to play female Space Marines skinned as Battle Sisters. The weapon choices aren't THAT different and they already said that the other imperial factions would just be lumped together anyway.
I don't think it's all that dissimilar. Same broad shoulders (though not as far down the arm), same backpack, same love of accessories... As for rules wise, they used to have the same save in the TT, unless they changed it in the newer editions. Either way, the difference isn't overwhelming and we get two factions on release with female characters. Three if they do the same with Chaos.
Now how many main female character are in the: Halo, CoD, Battle Field, Modern Warfare, Gear of War, Quak, Unreal (a few). Eldar - male / female Orcs - A sexual and a spore. So technically gender natural so they count for both Half of the available races on launch feature a female /non male. SoB have a different toughness and armor save as well. They also use faith points, and mass flamers. Good idea, but they need their own chapter. Although a Heavy flamer as a Retribution squad sounds tight.
Welcome aboard den ya git! Yaz moight see meze pokin around tha Eldar forumz now an again, I'z loik tha ambassador ov sortz..... anywho welkom to dis wee patch ov hell, see ya around