Could you please tell what's so difficult in this? I mean, seems rather simple to me considering all other efforts done to make the distro work as fluently as it does.. I don't know nothing about the current installation procedure, but I suppose it's rather simple image copying from dvd to hd, and so the problem lies in managing dependencies and keeping portage acknowledged about installed stuff.
Installation therefore should be based on portage, where installable packages are binary ebuilds. If that's not doable, then the installation image could be splitted into non-debendable parts, like core containing common stuff for all other packages, desktop-environment-x and its libraries, desktop-environment-x'applications (by gategories maybe), desktop-environment-y and its.... and so on. This would lead something like there's going on with k/x/?ubuntu, not as modular and less manageable but improvement.
Just a thought. Shoot me down. Softly.