I think getting "BAM" functionality into jBPM would be excellent.
In the past, I've ended up using database views over the jbpm tables to provide a picture of how many process instances are in which state (and how long they've been there).
One thing that I think is missing from the current discussion is the idea of the "owner" of a process instance. If you know who owns a process instance it becomes easy to do queries like "show me the current state of all the process instances I own with a task that is past its due date" - which is very useful for people who are trying to manage the overall business process.
I'd also caution against assuming that historical "BI" functionality has to be included with BAM. It is my experience that for "busy" systems, BI reporting is carried out against a dedicated reporting database, so that complex and slow running queries do not "clog" the business critical transactional database. The BI reporting will be performed over a large set of data, not just data captured by jBPM (it may pull in data from other sources as well, such as webserver logs) - which means the whole BI piece goes beyond the scope of jBPM... ?