Markdown is a convenient but deeply limited markup language with only a small subset of html's features. And yes, limitations are good because we want documents not web apps, etc, etc, but I mean "images can't have captions" limited, "navigation bars don't exist" limited. Actual important features of html don't exist in markdown, which is why almost every markdown platform ends up adding extensions and shortcodes. Wh…
Markdown is deeply limited, that's true, but I often think that there is just a tiny bit of syntax lacking to make it just fine. Some actually is implemented in software like Pandoc or RedCarpet, there are a couple of ways to make tables (some better than others), LaTeX can be employed for formulas, some implementations have checklists, strikethrough, etc. It's just poorly standartized — and the spirit of original proposal (and misleading name) is at fault here as well, since later attempts to invent a standard mean very little when there is a dozen of different common implementations and not a single one is reasonably complete.
By the way, the fact that HTML was supposed to serve as an addition to Markdown doesn't help: you just cannot allow people to submit arbitrary HTML everywhere where something like Markdown is needed. To use it in comments on a forum you need to fully parse it anyway, explicitly enabling or disabling different features of some ubiquitous "full implementation".
Obviously, you cannot make an atrocity like a modern landing page in Markdown+. But… ok, I shouldn't be judgemental and claim such atrocities shouldn't exist — they can, but most blogs, forums (such as this one), etc. — really could have been just "viewer programs" of some standardized format, much more restrictive than HTML+CSS+JS, but a little less limited than Markdown.
All of this isn't very much related to the original topic, but seriously, I dream of some better version of Markdown someday becoming a de-facto standard markup language for all forums, messengers, blogging engines, whatever the general name for Jira is… You know what I mean.
I don't really have a solution, it just really feels like there shouldn't be that many additional features. A couple more of emphasis options, a couple less ways to do the same thing (I mean, it's stupid to convert all of */-/+ to the same elements), colors, better image embeddings (with captions), sidenotes, better ways to handle formulas (there are enough dedicated literals in Unicode to construct most simple formulas without the need for LaTeX, but they still need to be parsed to be rendered pretty) and simple UML-like stuff… I'm pretty sure the comprehensive list of features for 6-σ usecases cannot be THAT huge. Big, yes. Not endless. And most features surely have some "plain-text" (or very light special syntax) representations.
I realize that it was pretty much the intention behind HTML + CSS. But HTML + CSS stopped being that a very, very long time ago. 30 years have passed. By now, we should have a little better sense of what's needed to write & render most texts.