Your comments

I think Markdown is easy, too.

It was design to be easy and human reliability even in plain text.

With BBCode you have more WYSIWYG and a Write-Click-WordLike-GUI.

I agree you can do more with BBCode, but do you really need this?

Now days with the right Markdown-Plugins you can almost do, what you can do with BBCode e.g. Tables.

With Markdown you can type your Content right down without using the Editor.

If you use the BBCode HTML it's more pain and overhead to write.

I'm not sure what produce more (HTML) Footprint, cuz of Mobile, Flatdesign, ...

More important is to disallow HTML+JS to avoid XSS.

But I don't disagree to BBCode, I think both can exist.

If I need to write something simple and quick, I use Markdown, but if I need more complex Content I use BBCode.

That would be great.

But converting between each other would be a bad idea, if BBCode can do more then Markdown and Markdown don't support it.

I think the future would be show what users need and use the most.

For me Markdown is enough.