While I agree in principle, in practice the result would probably be terrible.
Just look at tables in GFM, which mostly were designed as you propose. They look like tables even before rendering, however the experience of actually creating and editing the tables is not fun at all.
I have a horse in this race (co-founder of a markdown-based note-taking app) and to me, the benefit of markdown is easy + explicit editing, not that it looks the same in plain text vs rendered.
I agree with you on Markdown tables. They're pretty horrendous to write by hand. I wonder if there's an alternative that would be easier? Maybe something that's essentially a CSV embedded in a Markdown file? I'm sure CSV has some edge cases that could be a problem, but it's probably a decent 80/20 (or better) solution if you just want to make a quick table by hand.
CSV are no better than markdown tables to edit by hand. However they’re convenient in that you don’t have to do that and can use a spreadsheet.
rST allows using a csv as a table and that’s mighty convenient. An other thing that’s mighty convenient is rST allows rendering a nested list as a table. It’s not amazing because each list item is a row rather than a column, but it is a lot less confusing than having to edit a markdown table if you’re not in a table-aware editor.
Worth noting that Emacs makes Markdown tables pretty easy to create and format cleanly for plain text viewing, and other editors may/could/should do the same.
I use Sublime almost 100% now-a-days; and, it for sure isn't as nice as Emacs for editing MD tables, but multi-cursor editing does about 80% of the heavy-lifting for MD tables. I guess I could conjecture someone objecting about "really big" tables and editing them ... but, is MD really the right choice in that case?
I personally think the bottom line here is that markdown simply isn't intended nor well suited for anything complex such as tables or diagrams or any such things that have been bolted on afterwards.
Just look at tables in GFM, which mostly were designed as you propose. They look like tables even before rendering, however the experience of actually creating and editing the tables is not fun at all.
I have a horse in this race (co-founder of a markdown-based note-taking app) and to me, the benefit of markdown is easy + explicit editing, not that it looks the same in plain text vs rendered.