I'm not sure if having a reasonable opportunity to read someone their rights, then choosing not to, is in the spirit of the public safety exception. Public danger alone can't be the reason, since the whole reason for criminal law in the first place is to protect the public from danger. Interested if an actual lawyer could clarify.
I think it comes down to the quote in the OP "So while it may sound weird, it turns out that obtaining a statement outside Miranda but not admitting it in court is lawful."
Your assuming the motivation is to violate the suspect's rights. It might not be -- there might be a clear and reasonable aim to find out if there are others involved.
The authorities probably has a lot of evidence & a strong case without the interrogation. That they want to question the suspect about other parties or networks seems reasonable.
It's a tactic, but perhaps their primary motivation isn't to interrogate to get a conviction -- it's to garner a wider net of information. In that case, the Miranda & having the suspect clam up would be a hinderance.
Since this is the first time I can remember hearing of law enforcement announce that Miranda was not given tells me that he's already said something and they're just getting ahead of the cycle by putting the rationale out there.
It seems that your rationale requires that you have heard of a lot of similar cases. Can you recall the other similar cases you have heard of where LEOs did not mention mirandizing the suspect?
https://en.wikipedia.org/wiki/Miranda_warning#Public_safety_...
I'm not sure if having a reasonable opportunity to read someone their rights, then choosing not to, is in the spirit of the public safety exception. Public danger alone can't be the reason, since the whole reason for criminal law in the first place is to protect the public from danger. Interested if an actual lawyer could clarify.