Due to the latest confusion in the future of jBPM and the unclear continuation of jBPM 4.x we will start a initiative to create an abstraction layer around the engine together with a couple of our customers (we are involved in a lot of jBPM projects, most of them in Germany, and most of them still jbpm 3.x, but productive :-)). So in my past I saw already a lot of these (project specific) abstractions, so I think it is time to bring it to the next level (puh, seems I hang around with too much marketing guys these days ;-)).
I wrote a first blog entry for it yesterday: http://www.bpm-guide.de/2010/04/17/abstracting-the-process-engine/
Depending on the concrete projects joining we will provide a binding to jBPM 3 and maybe jbpm 4 soon. And maybe jbpm 5 some day :-) I try to discuss a draft of it next week with the involved parties...