I am generally sympathetic with calls to replace LaTeX with something else. LaTeX has terrible defaults, Unicode and font support is a constant problem, the syntax is deliberately obfuscatory, and actual generation is painfully slow (probably because the whole thing is a big pasta factory of interpreted code instead of a single static library).
But at the same time, I don’t think Markdown is really good enough for LaTeX. Of course one can use Pandoc to generate LaTeX from Markdown notes, and its output is often a decent thing to copy and paste into your LaTeX document. But Markdown just doesn’t solve any of the issues I mention, except making the syntax a tad more WYSIWYG than it would be otherwise. And Markdown is quite a bit worse at one thing: the extended syntax for tables is very hard to key in and still much less expressive than LaTeX’s actually pretty rational tabular environment.