Well, it's not easy to provide UI controls to switch the WYSIWYG editor on and off at will, but you can rip it out of the CMS altogether for a specific site, and provide a simple textarea.

To get you started, put the following into your Page class.

function getCMSFields() {
$fields = parent::getCMSFields();
$fields->removeFieldFromTab("Root.Content.Main", "Content");
$fields->addFieldToTab("Root.Content.Main", new TextareaField("Content"));
}

Polish work, such as removing the TinyMCE toolbar, is left as an exercise for the reader. Looking at cms/templates/includes/CMSMain_right.ss should get you started.

We are working on extending our 'administration system' beyond the requirements of simple content management, and in time, this will probably lead to reduced coupling with TinyMCE.

However, one thing that we will *NEVER* do is design a CMS authoring interface for programmers. Our CMS is designed for people are familiar with common business applications such as Word and Outlook. Admin & communications staff are a good example of this.