I like the idea of using the browser for the user interface. But I agree that it is not so good to have to use HTML, CSS, and JavaScript (as well as Suneido).
For multiple connections, it is better to use HttpServer and http:// links instead of the suneido:// protocol. And if you want to handle a lot of connections then jSuneido (the Java version) is better because it is multi-threaded and will take advantage of multiple cores and more memory with 64 bit.
The Eclipse RAP project is interesting – they have implemented SWT on the browser so you can run the same user interface on the desktop or the browser. Google Web Toolkit (GWT) is another interesting approach where they translate Java to JavaScript to run on the browser.