[Cossolus]

I think that's the most important feature, and would give your site an advantage to using a wiki. Providing/exposing 'semantic structure' in documents and separating style from structure is cool, but I don't think that's a problem that people are clamoring to have solved, anymore than it's already solved by various markup technologies.

A wiki that can exports its content as professional grade PDF files suitable for publishing would be awesome, but that's a major feature, and my humble advice would be to see if that's doable WELL before you do anything else.

I would actually be interested to know if anything already does that...

[_mql]

The problem I see with markup, is that for-non technical people it's hard to understand and use. I think they would rather prefer a WYSIWYG-style. Wiki-style-markup isn't for everyone. So that's why I chose WYSIWYG editing, but with restricting it to just semantical annotations.

Regarding PDF. I totally see your point. And it has high priority. I got offered some help by Kevin Lynagh (http://www.dirigibleflightcraft.com/index.html) already. He'd help with implementing LaTeX/PDF export of Substance Documents. You're invited to join too :)