Here's what I can think of that are barriers to tight JBPM integration.
* JBPM Designer doesn't support pluggable action/node types (JBPM core does through node.types.xml). I know nothing about eclipse or how hard this would be.
* JBPM nodes/actions don't support lifecycle. We need start/stop for both nodes and actions. This may be solvable by MCizing/beanitizing the JBPM object model and rewriting the JBPM XML parser so that it creates MC bean metadata.
* Different Message interfaces. ESB has org.jboss.soa.esb.Message. JBPM has Token. Both have different ways at getting at metadata and conversational data. I think we can solve this problem with pluggable node/action types that JBPM core provides (so long as the designer supports it) as well as using Seam bijection. If all our ESB actions are written in terms of Seam bijection, then maybe we can plug/play with JBPM.
The end goal of all of this is to be able to blur ESB, JBPM, and Web flow so that ESB actions and glue can be used anywhere within a business process or webflow. Vice versa too. ESB can embed workflow within its definitions.
There was a ESB/jBPM collective team meeting last week where a lot of the integration issues were covered in depth. I wasn't at it (was with you, remember ;-) but from what I hear it went very well and we've got coordinated agreements from the teams on what's possible now and going forward. At some point the conclusions will be written up (wiki I think) and you can take a look.