Hacker News is interesting in that it somewhat splits the difference. Post and comments are both represented by "itemID" (and there's no distinction between What Is a Post and What Is a Comment that can be made simply based on the contentID). For example, I'm currently replying to itemID 36329954.

But profile identifiers are semantically-sensible strings. In your case "blehn", in mine, "dredmorbius".

(There may well be, and all but certainly is, an internal userID or similar, but it's not exposed at least through the Web interface, I've not looked at the API in detail for this.)

This means, amongst other things, that it's possible to traverse all extant HN posts either sequentially (beginning with <https://news.ycombinator.com/item?id=1>) or randomly (say, by generating a list and sorting it randomly, or by algorithmically calculating itemIDs without repetition).

Google+ did this for both posts and profile IDs, assigning each what appeared to be a hash, which was not sequential, and was sparsely filled. Profile names / labels could be reassigned independently of that identifier (with limits as to how frequently this was allowed), and multiple profiles with the same name were permitted, addressing the "John Smith" or "Maria Gonzalez" problems (commonly-occurring names where all but the first-arriving party must choose something different). It was not possible to trivially traverse the (large, hashed) namespace, though Google being Google these were itemised in some 50,000 or so sitemap files, a fact I exploited to some benefit.[1]

In the case of a discussion site in which forum identifiers are arbitrary but labels are semantic, issues such as discovery, relevance, and trust would be mediated by some other mechanism. Note that the extant Reddit practice already has numerous issues, e.g., /r/ClimateChange is a sub devoted to denialism (under the pretext of "rational" discussion and skepticism) whilst the scientific consensus is far better represented at /r/climate.[2]

What the intermediation of arbitrary identifiers vs. descriptive labels provides is defence against squatting or appropriation of high-value, high-salience identifiers by malevolent actors. If your label is independent of your description and reputation, it's less tractable as a means of disinformation or propaganda.

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Notes:

1. "Estimating G+ User Activity: 4-6 million active posters in January 2015 to date" <https://ello.co/dredmorbius/post/naya9wqdemiovuvwvoyquq>

2. And regards the present Reddit Blackout, I'll note that the denialist subreddit is available, the consensus subreddit is blacked out. Which raises interesting points about the challenges of adhering to moral principles in an immoral world. I also note that ClimateChange's long-standing moderator appears to have been inactive for the past 9 months, though they are still listed as chef moderator. It's possivle, though uncertain, that former characterisation of that sub may well have changed.