I do see merits in JBoss Logging when compared to SLF4J.
However I would love the JBoss Logging team to contribute directly and influence the direction of SLF4J (the API, not implementation) than to create a competing API (of which there are overlap, and JBoss Logging adds some powerful features to the API).
JBoss Logging can still retain its own logging implementation, much like the way Logback is one implementation of SLF4J API.
My suggestion is that the JBoss should submit API improvements to SLF4J, so that on the API level it everybody can use the same rich API that JBoss Logging provided in SLF4J. This would benefit both JBoss and SLF4J communities.