Earlier quoted context omitted.
> There are also other markup-languages, which use other established syntax from the old times. Would you care to share some examples? I'm genuinely interested, while nothing obvious that would fit this description comes to my mind.
AsciiDoc, reStructuredText, textile, org-mode, they all have to some degree such syntax. Or just read old usenet-archives, FAQs and such. It's natural to do it if your aim is to be lightweight and readable. You just happen to use the elements you have at hand. And people did that, wrote all kind of texts and documents in ascii with made-up syntax on the spot, for usenet, e-mail, ftp-servers, etc. It's hard to say tha…
Most of them have fallen into disuse following the ascendency of markdown, but anyone who was on the internet in the mid-aughts will remember textile and creole, they were major contenders in the CMS and wiki space respectively (IIRC).