Jini is released under the SCSL which prevents us
from openly distributing it.
Why do you need Jini when you have JavaGroups ? :-)
The clustering subsystem provides a number of services which you could use to dynamically discover services, e.g. HAJNDI, or DistributedStateManager (which is essentially a replicated hashmap).
I'm working on a replicated cache (check out org.jboss.cache), which will have the form of a tree (similar to org.javagroups.blocks.ReplicatedTree). You could use this as a decentralized non-spof registry, a la JavaSpaces.
probably no reason we can't provide JBoss detection by using the Jini Location service (reggie). however, i'm not sure what it really buys you ...