One of the promises of XBLinJS was that you'd be able to use it for more than just HTML. I have to admit that at the time, I was only about 80% certain that I could do that. But I saw this article, and combined with the recent market successes of Firefox and some personal projects of interest that could be used there, I took a few hours tonight and tried to create an SVG Widget. (Note that the real story with FireFox is they plan to "turn on" the SVG support for everybody in 1.1; it has existed for a while, but in a highly experimental form.)
I succeeded; it turns out my DOM2 support (via DOM2Flavor) had several serious shortcomings, so probably I was the only one who could get it to work, but by and large I created an SVG widget today. It is a blue rectangle that, when clicked, grows vertically by 10 pixels. It may not be exciting but it does provide a proof of concept, and it is directly part of an XHTML page, not an embedded object. (I am not certain if XBLinJS can be used on SVG images embedded via object tags.)
That said, it seems likely to me that my next major conversion job is to convert a drag-and-drop library into XBLinJS, and experiment with some SVG stuff for 0.5, hopefully with the same drag-and-drop libraries working both for HTML and for SVG. (Theoretically it can be done, but we'll see.)
A 0.4.1 release will likely be made over the next couple of days to include the at-least-partially-functional DOM2 support, and some other minor bug fixes I encountered along the way. The demo will also be updated, even though it is likely the SVG support will only work in a very small number of Mozilla installations.