The future of web is with the modern web languages and its not hard to anticipate the adoption rate. Over the last year, 20% of the Top websites have moved to modern web languages such as HTML5, CSS3 and use DOM extensively for various transitions, and rendering techniques.
Your HTML5 webapp can be powerful enough to compete with the desktop version, but you might be limited byt eh performance advantages as your app runs in the browser, instead of native code. But good web development practices can definitely help you reach there.
Pau irish, a Google Employee, gets into details on how you can cut down the processing required for creating common things in Webapps: HTML5, CSS. He concentrates on CSS reflows, taking benefits of hardware aceclerated CSS, optimiations for Animations, and benchmarking techniques.
You can also checkout the full series of Microsoft’s presentation from MIX10 about HTML5 High-Performance best practices: