Btrfs devel - Jul 2012 - State of "Hot data tracking and moving to faster devices" functionality ?

https://btrfs.wiki.kernel.org/index.php?title=Main_Page advertises "Hot 
data tracking and moving to faster devices" but as far as I could find 
(http://permalink.gmane.org/gmane.comp.file-systems.btrfs/15884) the 
patches have never been merged. What is known about the future of this 
sort of performance enhancement in BTRFS ?
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