Best I can tell, they already encrypt a whole load more and are ready to encrypt everything. When setting up a new iPhone, I’m asked to enter my Apple ID, password, approve via an existing device, provide 2FA and then provide the PIN or password of that existing device. After all that, access is granted. To me, this suggests they’re already encrypting in such a way that while it may be brute force-able, it’s unlikely to be data they can read by default.