[popcornmix]

From Xbian:
"we've changed the default filesystem from EXT4 to BTRFS. This optimizes the write and read speed and so increases the performance".

Would this change bring benefits to rbej builds too?

It could do. Personally I'd be more tempted by f2fs.
OpenElec will be less affected by the filesystem choice than Xbian/Raspbmc as it runs from a squashfs - only the user data (e.g. cached thumbnails) will be affected.
May be worthwhile though.