This is being called "the biggest leak in history", which is probably not true (remember when Gizmodo got its grubby paws on the iPhone 4?). But it's likely the biggest leak in Apple software history. Motherboard says it...
could pave the way for hackers and security researchers to find vulnerabilities in iOS and make iPhone jailbreaks easier to achieve.
That's plausible. iBoot is responsible for ensuring a trusted boot of the O/S. The specific version posted was from iOS 9, but this portion of code probably doesn't get updated as often as the Music app, so it's likely still relevant.
Apple promptly posted a DMCA takedown request, and the source code is no longer publicly available. But we developers know all to well that once source code is made public, there's no taking it private again.