TWiki has a "raw view" that allows you to see the raw wiki markup for that topic. I use it alot: troubleshooting formatting issues, or if I want to grab the topic for editing in my favorite editor, or if someone else has the topic locked for editing, I can still grab it and edit it, then wait until it''s unlocked to copy''n''paste.
Would anyone else find this useful?
Does the ''plain text'' editor work the same for you as the TWiki raw view or were you looking for something more?
The idea of being able to get the raw wiki markup even when someone else is editing does sound like a nice feature.