I like the new Sister stuff. Looks great. Does it belong in 40k? No I don't think so. They seem to be better placed in their Kill Team or even Necromunda games. 40k seems to be confused on what kind of game it is. Back in 2nd Edition which was more skirmish, Sisters and Arbites made a little more sense, but in a game with typically masses of military units, I don't understand how the Sisters are supposed to fit in. It seems ridiculous they would have huge masses of troops, and I think they are better as part of the Grey Knight/Inquisitor like organization. And if you are going to develop armies with smaller organization structures, then what is stopping them from putting in Necromunda gangs in 40k? Might as well.
I haven't followed the rumors much though, so I don't really know what GW has planned. But if I see the Sisters in that Apocalypse game then I think it will be dumb.