I'm having a little trouble understanding the scope of your question. At the bottom of our WikiPlus pages we use a control to render all the recent discussions for the page. There is no "threaded" view on the WikiPlus page itself.
If you wish to see a threaded/flat view on the actual WikiPlus page, then I would recommend adding a list view webpart, pointing it to the discussion folder for the WikiPlus page and setting the view to threaded.
An alternative could also be to edit the following file:
C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\14\TEMPLATE\CONTROLTEMPLATES\WikiPlusTemplates.ascx
There is a rendering template in ascx file called "ResentDiscussionsForm" that handles how the posts are displayed at the bottom of the WikiPlus pages. It is possible to change this template so that it has your own custom control, or uses a list view webpart to show a threaded view of the discussions of the page.
Product Development Manager