alt Hacker NewsBloomberg's claims sound like science fiction: https://www.servethehome.com/investigating-implausible-bloom...
Bloomberg's tech coverage is not great from what I've seen. Last year they published a video which was intended to investigate GPUs being smuggled into China, but they couldn't get access to a data center so they basically said we don't know if it's true or not. Meanwhile an independent Youtuber with a fraction of the resources actually met and filmed the smugglers and the middlemen brokering the sales between them and the data centers. Bloomberg responded by filing a DMCA takedown of that video.
What Bloomberg proposed - sniffing the TTL signal between BMC and boot ROM and flipping a few bits in transit - is far from science fiction. It would be easy to implement in the smallest of microcontrollers using just a few lines of code: a ring buffer to store the last N bits observed, and a trigger for output upon observing the desired bits. 256 bytes of ROM would probably be plenty. Appropriately tiny microcontrollers can also power themselves parasitically from the signal voltage as https://en.wikipedia.org/wiki/1-Wire chips do.
Something similar has been done in many video game console mod chips. IIRC, some of the mod chips manage it on an encrypted bus (which Bloomberg's claims do not require).