My two cents:
1) The availability of a simple clustering strategy for upcoming version of JBPM is a mandatory asset to gain acceptance of JBPM in the enterprise world. Is not possible to have to resort to hack or something when in the JBoss products lineup there are at least a couple of distributed cache solution that can be adopted to allow clustering
2) The name itself "loadStatefulKnowledgeSession" has the implicit meaning that the session cannot be easily shared, if the session is "stateful" then it goes against the "stateless" requirement that are behind a "pure" cluster solution. There should be a way to have a different provider or to configure the JPAKnowledgeService in a way that enables an easy clustering solution and manage concurrency without resorting to database locking and retries, like having a shared cache mechanism to share the knowledge session across nodes in a way that is fault tolerant, highly available and has good performance
I do not know it there is an easy way to push for a solution or to create a Jira request so that it can be voted but, from my point of view, this other enterprisey requirements are the ones that need to be pushed to make JBPM suitable for a larger adoption.
Regards
Massimo