Latino Review spoke to Chloë Grace Moretz while promoting Carrie and she relayed:
No, no rumors I don’t know how they get started.
But it would be great to be a part of it. I don’t think Disney doesn’t know what’s really going to happen.
I don’t even think they cast the principle roles yet.

It makes me wonder if her assumption is based on knowing that people are still reading for those roles. Like Ronan just said, everybody has read for those parts. It could also be because she has not been officially rejected yet. But that’s all speculation, of course.

And just because we have this image on file as well:

All of this kind of fits with the Lucasfilm line that when they know something, we’ll know something. It is looking more and more like they have not cast anyone yet and there are no secrets (which is what I believe). Maybe they’re trying to get a good ensemble together and that will determine who gets cast and who does not? If they are going for a lighter tone this time, the actors will need to be able to play off one another. Just a theory.