Part of the problem is that people don't really grok the point of Markdown. There's a reason it doesn't support tables, or a syntax for making the kind of language used in a code snippet. The point of Markdown is to mimic the conventions of ASCII-text email, both to make writing it as natural as possible, and to make Markdown pleasant to read in both ASCII and HTML.
If you want something more featureful than Markdown, the problem isn't Markdown; it's that you're using the wrong tool for the job.
org-mode in emacs supports tables, and it's ASCII-based.
Here's an example, displayed exactly how you would see it marked up in org-mode syntax in emacs:
|-----+-------|
| Key | Value |
|-----+-------|
| 00 | foo |
| 01 | bar |
|-----+-------|
Org-mode is a beast. A fantastic beast, much like Emacs itself. You dive in, but there's always more to learn. Some things may be for you and some things don't. Everyone should give it a try.
A little known fact, even among most org-users: Github can render org-mode files to HTML directly if checked into a repo, thus you can write your README files as org-files.
Shameless example: https://github.com/josteink/csharp-mode/blob/master/README.o...
This alone was enough to make me drop Markdown as my go-to format for semi-formatted text-files.
A subtle killer feature here is org-babel. You can embed proper code in your text-files and have your editor (at least Emacs) understand them as such. Which makes it excellent for writing technical documentation for projects where code is involved.
They also support ASCIIDoc, ReST, MediaWiki markup, Creole, etc.