I was wondering about a few things.
jME phyiscs 2 is gonna be plugable(like phyiscs engine wise)
if so how will you deal with stuff like one engine having features another doesn't will physics 2 be limited to the features of the engine with the fewest number of features
Or will there be features that are only engine specific put in with common engine features?
Could i get a progress check on physics 2? Your entering beta 2 how much coding would you say you have done?
If i think of any more questions i'll be sure to bug you with them.
Perhaps it would be beneficial to check the source out and take a look at it yourself. 
darkfrog
Yes, the API is physics engine 'independent'. Already for the current (ODE) implementation this means that you can specify things with the API that the implementation cannot handle (which results in an UnsupportedOperationException). In the ODE case these are primarily joint configurations (where ODE is quite limited). So the API should not be the intersection but the superset of features. But I examined most popular freely available physics engines (ODE, Newton, PhysX) and they do not differ that much in functionality.
Regarding progress - well what do you want to know? How much coding, err: 7000 loc java written, 13000 loc java improved and a refactored, several thousands of nasty c and c++ code understood and debugged, Makefiles corrected and newly written… well does this say anything about the actual progress? I don't think so. It takes much more time to write less code…
Did you take a look at the readme.txt? It contains info about current features and what is planned (and what would be nice but probably never implemented).