With support from leading stake holders(read application server and integration solutions vendors) like IBM, BEA (both of them had originally proposed SCA), Oracle, SUN( a new recruit) and many others, SCA(Service Component Architecture) has picked up a great momentum . The specifications are still being evolved to become more mature and complete. Oracle is actively involved in the process. BTW SCA specifications are yet to participate in any standardization process. When it comes closer to standardization, you may see SCA based SOA suites from various vendors including, of course, Oracle.
It would be interesting to see how the story of JBI and SCA would evolve. Instead of JBI vs SCA battle, in long term, I would expect some sort of convergence or integration. It might be a wishful thinking on my part. Please note that JBI is part of JSR/JCP standardization while SCA would not be subjected to the same standardization process. SCA is not a "Java only" specs. So it might be submitted to Oasis or W3C.
A different standardization processes would be one of the reasons for both JBI and SCA not converging to a level of an unified specifications. But I expect vendors to be innovative to develop their own flavor of integration or co-existence of JBI and SCA.
Just to complicate the matter, it would be interesting to note that Microsoft would continue to promote yet another direction with its Windows Communication Foundation(WCF).