Disk layout for XO-1.5

[NoiseEHC]

>
> Once BTRFS is mature, yum learns to snapshot-upgrade-or-revert and we
> switch to that combo, we will be able to retire olpc-update, the
> symlink trees and the fancy overlays.
>   
Do you have a prediction (I mean an educated guess) about when will 
BTRFS be mature? What I heard last time that they had to change the on 
disk layout so I do not know why do you seek for example firmware 
support for BTRFS. (I am really just interested in some roadmap.)