Dimitris, please comment with the official answer. :)
I'd think there'd be no problem upgrading across minor releases if we
went from 5.0.x to 5.1.0, but there would likely be a problem if we went
from 5.0.0 to 5.0.1.
Correct.
Either way, this points to a larger issue where it's unclear what
the
big picture AS roadmap is. Do we want to do a bunch of 5.0.x releases,
or fairly shortly after 5.0.0 go to a 5.1.0?
That's not clear yet. Chances are, we'll need a couple of point releases first.
As far as I'm concerned we can go with jgroups 2.6 if
a) Brian is ok
b) The JBoss Messaging team are ok
c) 2.6 is ready for the AS5 CR release
For AS Beta3 we should upgrade to 2.5, ASAP.