Have seen:
http://confluence.atlassian.com/display/CONFDEV/Preparing+for+Confluence+4.0
http://confluence.atlassian.com/display/DOC/Confluence+4.0+Editor+FAQ#Confluence4.0EditorFAQ-WhyisAtlassianintroducinganeweditor%3F

And participated in discussion about the removal of the full-page wiki markup editor here:
http://forums.atlassian.com/thread.jspa?threadID=51646

I think I understand the reasons why the wiki markup editor for the full page's content is being removed.

I also understand that Atlassian is striving to make the new editor as faster or faster than using wiki markup.

I further understand that Atlassian is planning on providing a way to insert wiki markup via the new editor, but just not a way to edit the whole page in wiki markup.

However, I'd still like to see a way to edit all of a page's content in wiki markup, rather than just a way to insert wiki markup into the page. This could be done through an optional plugin, but it would be nice if it were provided by Atlassian and perhaps included by default in the Confluence release.

Even if this feature isn't included in the first version of 4.0, I think it would be a good (re)addition in a future release. In addition, it would be nice to enable this in other Atlassian products (not just as a Confluence plugin), since I prefer wiki markup in Jira as well.