What about being folded into the Imperial Guard codex?
I'm not suggesting that I would support this. It might even be enough to get me to sell out of Sisters, to be honest. However, with this new trend towards creating supplemental codices, I could see how it might be a solution to GW's Sisters problem.
Think about it:
• The Ecclesiarchy is already deeply involved the Guard, and an ecclesiarchy priest is one of the HQs you can take in a Guard army.
•*The Sisters have a statline that's a lot like the Guard's, except for a better BS and Save.
• The Acts of Faith system does a lot of the same stuff that the Orders system does, only not as well.
What I'm forseeing is Sisters of Battle as an in-codex option of what Space Marines allies provide from outside the codex, both in the fluff and on the table: small elite units supporting the main army by getting into close-ranged firefights, which they can survive thanks to their superior armor and skill.
If this were a just world, we wouldn't have to wait long to find out. Nobody - but nobody - needs an update as bad as the Sisters do right now.
So, what do you think? An interesting theory, or total nonsense?