Notably, NSA hasn't denied. But, I wouldn't expect them to - they aren't politicized like DHS, which also does not really have much of a relevant role is this sort of thing. DHS's primary role, IMO, is to make citizens feel secure. FEEL secure. And to trumpet the administration's viewpoints in it's areas of supposed expertise.
My experience with "management chips" is rather out of date, going back to the early 2000's when I was involved with high-frequency trading, and had a couple IBM (pre-Lenovo) servers installed on "wall street". I used to build my own Linux/Windows boxes, as well, and I think sometime not long after that they started appearing in consumer-oriented boards e.g. that you can buy at Fry's etc.
To educate a bit with admittedly out-of-date information...
Back in the day, it was a "management board" rather than chip (wasn't on the mother board yet). It basically let you do most anything you could do in person. It had a physically-separate Ethernet interface, as well as a serial port that could be connected to a phone modem. (Probably absent today!)
It was powered even when the rest of the motherboard was powered down. One of the things you could do from the management interface was to power the server on and off. (We also had an external power controller, BTW, that allowed us to physically cycle power to the server, as well as other equipment, router, etc.)
You could reboot, interact with BIOS boot, e.g. see BIOS messages, provide keyboard responses. You could boot from a remote "floppy" or "CD". You could load a new BIOS image, or other firmware images, again from a remote "floppy" or "CD". Load a processor firmware update if needed (I remember some multiplication bug or some-such...)
As a practical matter, all datacenter-deployed servers have such functionality today, but now built on to the motherboard.
Being able to "piggyback" somehow onto the management chip, then, could give one a great deal of power. And would not be so easily detected as a mod to the management chip itself. It might be disguised as e.g. a surface mount capacitor, which seems to be the implication suggested by the photos we have seen of the chip on the fingertip. (Which I assume is NOT an actual photo of the actual chip.)
One might alter firmware in the management chip itself, BIOS, other firmware, etc. but that would be easily detected by diagnostics.
As I understand it, this is not a chip for mass surveillance - and it's not a chip that's expected to do a lot of work. So, suggestions that it's "too small" are nonsense. The modest processor needed for this could easily be put in such a small package.
The "management bus" on these servers is serial, so there is not a need for a large lead count on the package. It wouldn't be that hard to make a 3-terminal device that looks like a 2-terminal device, with a hidden through-hole underneath, or even an inductive coupling. One might disguise the inductive coupling in the circuit board design cleverly so it is not so obvious as a little coil in one of the layers under the chip. There, now you have access to the management bus.
"Who, me? I'm just a power supply filter!"
-----
Not sure what the point was, but a couple people mentioned Apple and Microsoft's non-use of their own products. Unfortunately, neither makes suitable products. By Microsoft's own admission, BTW, > 50% of Azure servers are running Linux. Microsoft eats a bit of their own dog food, their Azure customers eat even less. In any case, Microsoft has no suitable hardware. (Racks of Surface tablets? Racks of X-Box, LOL! FWIW, though, when working at Sony a few years back, we actually DID have racks of Playstations! It was for a specific game, most servers were Linux.)
Mac Mini is in no way suitable for serious work in a datacenter. Underpowered, insufficient thermal design, and no management chip. (Yes, I know there are companies that offer racked Mac Minis.) Mac Pro is a poor match due to the goofy form factor, expense, and unused/unusable features (powerful GPU - if you need GPUs in a datacenter, you will have dedicated GPU boxes...).
---
I was curious what Alex Jones/Infowars had to say, since he was brought up. There's only one article there right now, buried, since that site right now is so single-issue on the Supreme Court right now. The article seems neutral, just reporting what Bloomberg and the companies are saying, and offers no opinions. But I suggest that Jones won't support the prevailing opinion being expressed here of "nothing to see here, move along!". If for no other reason than his feud with Apple/Tim Cook, and will use this as an opportunity to try to drag down Apple and Cook and brand him a liar.
Sometimes, I think Alex Jones may accidentally stumble into congruence with the truth. Will be an interesting show to watch!