It would seem to be a no-brainer that everyone who set up Extension:WYSIWYG would want this. I found it in an old FCKeditor installation. Add these four (4) lines to LocalSetting.php. New users will have WYSIWYG rich text editor as default while hiding wikitext editor. Use My Preferences page to undo, but why?
$wgDefaultUserOptions['riched_use_toggle'] = 0; $wgDefaultUserOptions['riched_start_disabled'] = 0; $wgDefaultUserOptions['riched_use_popup'] = 0; $wgDefaultUserOptions['riched_toggle_remember_state'] = 1;