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Seeing the massive overhaul of desktop concepts that is planned for Gnome 3.0, I'll guess this will be in Gnome long before 3.0 is even started.
My guess is 2.12 for cairo and som of the xcompmgr effects. Luminocity will probably leak some features into the 2.14 release. 2.16 will probably be 3.0 but that would mean that they will go long over the 6month release schedule.