What makes it possible now, is there a new mediatek bootrom vuln?

LLMs got powerful enough to implement much of what's missing from scratch. My guess is most older devices/bootloaders would soon be jailbroken/cracked in some... automated manner thanks to LLMs getting very powerful in reverse-engineering. There are plenty of implications we should think so.

Well, as of today I am not aware of any applicable bootchain exploits. Bootroms are small, and it's plausible for there to be no software bugs to find, regardless of how smart your LLM or human brain is (which is why fault injection modchips exist).