can't say if plugin_wiki is going to be updated further, but auth.wiki() is embedding quite a pack of features nonetheless. If you need more features, stick with plugin_wiki.
PS: plugin_wiki never had a WYSIWYG editor, just an editor with shortcuts buttons for bold, italics, list, etc. Markmin evolved into supporting nested lists, autolinks, etc, and the editor used (markitup) hasn't catched with the new improvements. On web2py > 2.1.1 there's the preview, though.