I'm pretty sure the construct <conditional modal verb> 'of' <past participle> is now accepted as grammatically correct, if not in "main" English (if such a thing exists), then at least in a majority of American dialects.
It's a double contraction, the word “of” doesn't appear at all: who'd've (who would -> who'd, would have -> would've, who'd + would've -> who'd've)
While you seem to admit that "main" English does not exist, you make the mistake of assuming that there is a "main" "accepted". Accepted by whom? The hordes on youtube or twitter certainly don't mind. And no, it is not part of an American dialect. An English litt. major could get reprimanded for using such spelling in their reports, even in America. It is a part of uneducated dialects all over the world.
Do you have a recognized dictionary agreeing with you that you can cite?
If not, you are wrong, simple as that. Using "of" instead of "have" in 2013 is a spelling mistake, period.
Dictionaries are descriptive, not proscriptive. It is possible for something to be correct, and dictionaries to have simply not caught up (or for it to be correct within a subculture the dictionaries do not cover). I agree with you that the former is not the case for "of" in place of "'ve", nor the latter in any subculture I am familiar with although that could certainly be my own lack of exposure. Regardless, it is worth knowing that many people will see it as an error and likely judge you for it.
It was a joke.
Or was it?
What makes you think that?
He presented it in a joking way, but it would be hard for me to believe that he or the larger kernel community hasn't been approached. Backdoors through cooperation would be the least effort and surest way to get in and stay in. Backdoors by stealth would risk discovery and removal.