There was a thread in the issue queue recently about adding a flag to textareas that the >module author could apply or not, which RTEs (TinyMCE, FCKeditor, etc.) could then hook >onto to decide where they should or should not be used.
This got me thinking that most of the time the problem with the WYSIWG editor being displayed all the time was that a lot of the time it screws up data that wasn't supposed to be HTML to start with. I've posted an alernative solution here that I've detailed in the following issue: http://drupal.org/node/87806 Basically it's to standardize how we tell the forms api and therefor contrib modules, what kind of data is supposed to be in the text area. Works for Rich Text editors, Color pickers, CSS editors, etc.