I'm planning to add a feature to equery list that allows you to list all atoms in a set. See pkgcore-0.5.9 pinspect pkgset for inspiration. Syntax will be: equery list @set_name RFC.
Holding off on this one until the Portage set API is stable.
Reopening to change resolution.
This is included in gentoolkit-0.3.0_rc10. example: # equery list @module-rebuild * Searching for @module-rebuild ... [IP-] [ ] app-emulation/virtualbox-modules-3.1.6:0 [IP-] [ ] x11-drivers/nvidia-drivers-195.36.15:0