Old, well-known feature of one of the most popular languages. I must be missing something, because I have no idea how this became a hacker "news" :)
What to Submit
On-Topic: Anything that good hackers would find interesting. That includes more than hacking and startups. If you had to reduce it to a sentence, the answer might be: anything that gratifies one's intellectual curiosity.
But thing you are talking about indeed recurs here. The way I typically guess is that new generations of programmers are coming up all the time and may be unfamiliar with some old stuff. Or, maybe even some experienced people who never happened to touch c or c++ [there are more of those as time goes on].
EDIT: I see several, just from doing a simple search against 'movq'
https://github.com/torvalds/linux/search?q=movq&unscoped_q=m...
I am not a kernel programmer, though, so I can't say whether it's being used in any capacity on modern, x64 systems or whether it's a compatibility mode for low-powered embedded architectures. Maybe someone more knowledgeable can chime in.
Things like: Hm, I need to swap my stack register and page table with this other process.
Or writing interrupt handlers.
Atomic operations and memory barriers used to be one of those things, but compiler extensions and new language standards have been catching up on some of that... Though to be honest a kernel will want enough control that it will likely still go outside the standard or extra compiler support for these anyway.