In 2005 TIBCO began investigating moving Designer to Eclipse. I was the main architect and development manager for this investigation under the working name luna. The project culminated in a demonstration at TIBCO's user conference, TUCON to get customer feedback. Luna included a replacement for designer's primary functionality as well as the basic BusinessWorks functionality, including process diagramming and debugging.
Luna was designer to hide some of the complexity of programming SWT behind a simpler data binding form toolkit. An example form from this kit can be seen in the screen shot below. Unfortunately more interesting screen shots are protected under confidentiality agreements.