Best web based SVG WYSIWYG
The only one I know is svg-edit. It is not nearly as powerful or mature as editors like CKEditor, TinyMCE or FCKEditor are in their field of application, and it won't be as simple to implement, since it is more a script like a component, and finally I don't know how easy it is to customize it.
But I heavily doubt that there is something similar with more comfort.
You might have a try here or here (just to mention, won't work in Internet Explorer - although the site states that it would work if you have Chrome Frame installed but I can't confirm that).
Maybe you could tell us how far this meets your requirements ;-)
One impressive example of a polished and very intuitive webbased "drawing" app is accidentsketch.com. Uses both svg and html.