Looks like Cate Blanchett may still be a possibility for Alien: Covenant.
At the Palm Springs International Film Festival Gala, Blanchett told USA Today that "I don't know what I'm going to do, actually," with regards to her next role and that she isn't currently locked-in for a role in Thor: Ragnarok as was previously reported.
Interestingly, this photo of her and Scott was taken at the very same festival recently. Blanchett of course also starred in Scott's "Robin Hood" so they have worked together before.