Your wish is my command, she said responding to IRC!
A compact list:
* No LCH color pickers and no LCH Hue-Chroma tool
(https://bugzilla.gnome.org/show_bug.cgi?id=749902)
* No Luminance blend mode
(https://bugzilla.gnome.org/show_bug.cgi?id=753163).
* No easy way to make Curves and Levels
There are some bug reports listed below that pertain to color management
and color mixing, that I would very much like to see be put on the
"milestone 2.10" list. Here's why:
I just posted a tutorial on using GIMP to make an illustration from a
photograph: