And then, I wonder if a wiki syntax still makes sense in the long run
if we have a WYSIWYG editor?

Currently the  WYSIWYG editor maintains but doesn't allow insertion of:
  • definition list and definitions
  • preformatted.
  • shout code formatting.
  • named anchors
  • mail to: links
  • annotated paragraphs
  • value links
  • annotations
  • verbatim
  • tables
  • embedded links
The editor could be extended to support the above - (I've experimented with providing a site map drop-down for internal links within the anchor dialog in the editor), but it would take some effort and would tie us more to a particular editor. At the moment I'm using YUIs editor - but most of the effort has been in the generic HTML parser rather than to a particular editor. To provide the above within the editor I think it would make sense to review the YUI editor decision, before committing to significant work - perhaps there are better options  - even YUI has a new editor (v3) in beta - but it is very incomplete when I looked (no toolbar).

Also it would be good to receive feedback from real-world use first. Can book content be edited with the Wysiwyg editor? Do people prefer using the Wysiwyg editor vs the wiki markup.