Is it possible to disable or customize the editor on a per-page basis? Let's say I have a page type for news items in which the user can only type plain text in the content field (and that the CMS only generates line breaks), or another page type with just a couple of options in the editor (bold, italic, links). Other page types can have a complete editor.

That would be quite difficult, because the toolbar is loaded when the CMS is first loaded. You could try making some custom javascript that's executed every time a page is loaded for editing, that disables/enables buttons as appropriate.