> put a clear, short summary first within said text [emphasis mine]

If I see a big block of text that I don't want to read—or don't have time to read—I'm not even going to read the first sentence.† I'm going to stick it in my ReadItLater queue and forget about it. If you don't want to say "tl;dr" specifically, fine, but do distinguish it from the text following it in some way.

Saying "Executive summary: X" is great: it'll be appreciated by the people who want it, and everyone else will just find it perhaps a bit dry in style, rather than actually insulting or offensive. Plus, the people who—based on your summary of the text to follow—turn out to not care to read any further, will have more time to do other things. (This is also what Email Subject lines are for. We use those for even the shortest of emails, don't we?)

† Note that I have this form of "wall-of-text disgust" because so few people write well enough to make reading the first few paragraphs a valid way to extract a summary of the text. Usually all I can pull from the first three paragraphs or so of an essay about, say, "how we solved the X problem," is a very detailed description of the X problem. It's a lot easier to convince people to write a one-sentence summary after the fact, than it is to teach them proper essay-writing style and convince them to rework everything they write to imbue it.

If you're afraid of turning people away with a "wall of text" or a "big block of text," avoid walls and big blocks.

Keep your introductory paragraphs short. In the rest of the text, put plenty of whitespace, and add internal headers and/or graphical elements where appropriate.

A web in which every essay begins with "executive summary" or "tl;dr" is a web with a lot of noise. These are needless terms from the worlds of MBAs and tech commenter communities, respectively. If you seek out people who have distinguished themselves at writing — for example, Paul Graham, Joel Spolsky, Steve Yegge, or Clark Shirky in the tech world — you'll notice that not one uses "tl;dr", "executive summary," etc. They simply put the information they want you to read first, FIRST.

These explicit summary headers, typically added as an afterthought, are tics of inexperienced writers. They're fine! They're not evil or anything. But they are ultimately less elegant and reader friendly than truly good, considered, well constructed and ordered paragraphs. Putting "executive summary" in front of the summary is like putting a comment like "#HERE WE LOOP OVER THE USER OBJECTS" in front of a simple loop: If something that simple wasn't obvious from the structure of the text (variable name, loop operator) then you're doing something wrong( users.foreach{|user| whatever} is self documenting whereas for(kljk=0;kljk < x.length;kljk++){foo = x[kljk];whatever} is not)

I'm not suggesting any of this isn't good advice. Yes, blending an introduction seamlessly into your writing will make you a better writer. But you're thinking as a producer of content here.

As a consumer of content, I can't hold myself to the standard of only reading things written by "people who have distinguished themselves at writing." If you're the only person who has written about X, and I'm researching X, I'm going to have to look at your article—at least to tell if I can safely not look at your article without having missed something important.

And good writing is hard: you're basically giving the creative equivalent to the obligatory advice of "eat less and exercise more." Yes, reworking and redrafting to achieve flow in your writing is a "good thing." It's something to strive for. But that doesn't mean that you can expect anyone to follow that advice just because they read a few paragraphs about it online. If they write much, they've likely already given it some thought—and it's a lack of willpower, not a lack of skill, that prevents them from editing their work as much as is necessary to get a result easily consumable by others.

An explicit "executive summary" line is a quick fix. It's something an amateur writer—one who doesn't practice writing as a craft, and has no desire to redraft—can use to make their writing less painful. It's asking much less of people—it's just a sentence, written after the fact, explaining what you just said—so it's probably something people would implement after seeing a conversation about it online and saying "oh, that could work."

Certainly, it's not as readable as good writing. But, for most people, it is more readable than whatever they had before, at much less cost.

(Also, I wouldn't mind if experienced writers included a call-out of some sort as well—not because it helps their prose at all, but rather just because I don't know if someone is an experienced writer until I actually dive into the body text, and by then I've already made my decision whether to read or not. Give me metadata.)