Here are my idea to improve grml even more!
1 Base it on testing (etch) Forget about unstable. There are enough distro's out there that are based on debian unstable. I found them all extremely volatile. You never knew what happens next after a dist-upgrade. Debian Etch on the other is up to date and without much problems. Another benefit from switching to Etch would that the developers have more time on their hand to focus on grml instead of fixing the errors in the unstable branch. And grml would also stand out more in the excessive amount of debian distro's available. So I say remove all unstable repositories! ;-) Users who really want could add them themselves but _i think that debian etch shoul be default.
_2 Add an option to install grub instead of lilo with grml2hd.
3 Less windowmanagers please Grml comes with a whole array of windowmanager most of which are in my opion not good enough. I think it will provide more clarity if the amount of windowmanger would be largely decreased. You seem focused on fluxbox and I would choose to make that one the default. Thanks to the debian apt-get system the other windowsmanagers are just an apt-get install away. You could make an oversight in the grml wiki of the available windowmanagers and their pro and cons.
I hope this information is helpfull in making grml a better product. Good luck!