David,
the home page there seems to be a little missleading - Ribbon is in fact an editor theme, not only a skin. Core tinyMCE has two themes, advanced and simple theme and ribbon should be used instead of default advanced theme...
I like the tabs of http://tinymce.swis.nl/demo on large screen - an option to select editor theme or skin or some preferred user preferences depending on needs and device might be another usability improvement. The tab idea with some larger buttons might work also in mobiles instead of filling 4 rows with tiny buttons that you can't click or touch.
Note also that the Ribbon files are using editor_template.js and theme files of TinyMCE 3.4.4 (2011-08-04) and current moodle 2.4 is using TinyMCE 3.5.7 (2012-09-20)
So it may have some bugs that have been fixed during the past year but basicly you should be able to change editor theme in lib/editor/tinymce/lib.php - and you can't use settings of advanced theme and ribbon theme at the same time. But you can switch editor themes also with some custom switchers...