> This creates exclusivity that somebody well-intentioned, but without an account [...] wouldn't be able to overcome.
Right, which is why we're generally opposed to restrictions on posting despite the headaches of being a public optionally-anonymous forum. We don't want to miss the chance of having, say, Alan Kay show up to comment on PARC, or someone who did a Ph.D. on a topic make an account to comment on it.
But posting to a monthly Who Is Hiring thread isn't really a serendipity thing. You have to know a bit about the community to do it—and if you do know a bit about the community, getting to 5 or 10 karma is easy. Even if it took a while, you wouldn't likely miss a thread, because they stay open for 2 weeks.
We've been getting a lot of emails from people asking how to post jobs in these threads, and although we always answer them, I sometimes do so with a sinking feeling that these are probably not quite the sort of posts the community wants to see more of. A very small karma threshold—just enough to be a speed bump—would probably take care of most of that. However I'm not attached to the idea.
Edit: I should add that we wouldn't do this without looking at the data first. "Looking at the data" in this case means looking at all the comments posted to those threads by accounts below a certain karma and/or age. If there were lots of high-quality posts in there, we wouldn't do it.