xfs-sources have less kernel configuration parameters - no Low Latency, no preempt kernel, etc. It just strange that I can compile kernel either with BeFS support or with XFS support but not both.
See: http://lists.gentoo.org/pipermail/gentoo-announce/2002-April/000152.html
We are working on adding XFS support to our default kernel... all our kernels offer different functionality. This really isn't a bug, but I understand, hear and will do what I can to satisfy your request.