I think depending on how this plays out, Apple might manage to earn some of the trust its users have in it, which would be pretty cool! But even cooler will be if we get full chain-of-custody audits, which I think will have to entail opening up some other bits of their stack
In particular, the cloud OS being open-source, if they make good on that commitment, will be incredibly valuable. My main concern right now is that if virtualization is employed in their actual deployment, there could be a backdoor that passes keys from secure enclaves in still-proprietary parts of the OSes running on user devices to a hypervisor we didn't audit that can access the containers. Surely people with more security expertise than me will have even better questions.
Maybe Apple will be responsive to feedback from researchers and this could lead to more of this toolchain being auditable. But even if we can't verify that their sanctioned use case is secure, the cloud OS could be a great step forward in secure inference and secure clouds, which people could independently host or build an independent derivative of
The worst case is still that they just don't actually do it, but it seems reasonably likely they'll follow through on at least that, and then the worst case becomes "Super informative open-source codebase for secure computing at scale just dropped" which is a great thing no matter how the other stuff goes