dev-java/jruby ebuild need Ruby 1.9 version, but there is only Ruby 2.0 in portage tree So, jruby cannot be built now. Also, in CDEPEND ">=dev-java/jnr-netdb-1.0:0" needs to be changed to ">=dev-java/jnr-netdb-1.0:0" as there is no jnr-netdb-1.0 with 0 slot in the tree
That's why it's still masked. :)