Why should you create SVG only web applications? Advantages of SVG only applications are flexiblity (you can control every single aspect of a SVG GUI element) and scalability (in SVG your userinterface elements are scalable as well). If you need a pixel-precise, scalable application, HTML is not very well suited, since HTML form elements don't scale well. SVG also potentially allows more sophisticated GUI elements than HTML provides, such as slider, dial knobs, complex colourpickers, etc. Disadvantages include complexity (more complex than using HTML form elements) and a potentially bad user experience, if your SVG GUI elements behave different than native GUI elements of the operating system the user is used to. Some browsers still don't support SVG to HTML or HTML to SVG communication. In that case you are sort of locked into doing everything with SVG in order to reach the broadest audience. Another advantage of creating SVG only applications is, that your applications also work in SVG viewers outside the webbrowser (e.g. Batik, eSVG or SVG embedded applications).