Kernfs is the sysfs logic that in turn can be taken advantage of by other subsystems in need of a virtual file-system with handling for device connect/disconnect, dynamic creation, and other attributes.
One of the motivators for making the sysfs logic independent is for the cgroups file-system but it's also anticipated that debugfs will move to being Kernfs-based in the future. Debugfs on kernfs should be a big improvement, but the code isn't yet ready. The Kernfs code is considered stable and ready for mainlining.
Kernfs for the mainline Linux kernel is happening as part of the core driver / sysfs Git pull request by Greg Kroah-Hartman for the Linux 3.14 release. This separating out of sysfs into Kernfs is not to be confused with NetBSD's Kernfs file-system.