If you want to do web based development for your UI then you should check out the Eclipse RAP project. The guys over at EclipseSource are the major contributors and they provide a bunch of material on their site. Mixing this with the web container that ships with Lotus Expeditor and Notes 8 could yield some pretty interesting off line applications written in web technologies.
This is a prime example where you could write your components using Web 2.0 (ajax) based content and then use the Browser App container to integrate those with your Lotus Notes 8.5 applications.
The RAP project enables developers to build rich, Ajax-enabled Web applications by using the Eclipse development model, plug-ins with the well known Eclipse workbench extension points, JFace, and a widget toolkit with SWT API (using qooxdoo for the client-side presentation).