Michael Natterer and Øyvind Kolås have pushed forward in recent weeks and finally making GIMP-on-GEGL finally become a reality. GEGL in GIMP was partially implemented in 2007 leading up to the GIMP 2.6 release, but even with the soon-to-come GIMP 2.8 it's still not fully leveraging GEGL.
GEGL allows for higher bit-depth images than what can currently be done with GIMP along with non-destructive editing and other features. The lead developer of GEGL has been Øyvind Kolås with original work on this library going back more than a decade.
As written about on Michael Natterer's blog, they were hacking on the code for weeks and ended up getting a GeglBuffer, which is backed by a GeglTileBackend, to use a legacy GIMP TileManager as its storage backend, which allowed for the rapid replacement of GIMP core with GEGL code.
In the three weeks, 90% of the GIMP application's core is ported to GEGL with just some remaining bits back. Plug-ins are also able to use the GEGL buffer tile back-end with the GIMP library.
Right now this massive GEGL enablement within GIMP is living in the goat-invasion branch (GEGL's mascot has been a five-legged goat), but will be merged to master once GIMP 2.8 is released. GIMP 2.10 will be fully GEGL-enabled, but let's hope it won't take many years for the GIMP 2.10 release like what's happened with GIMP 2.8.
GEGL 0.2.0 was also released at the beginning of this month. More information on the Generic Graphics Library is available from GEGL.org.