d-i work!
I'm at the Roan Mountian campground this week, and have been taking advantage of the peace and quiet and the resumption of d-i development to work on d-i.
I've fiddled with lots of parts of it today, but the big news is that I made d-i able to build images for the 2.6 kernel using initramfs. Besides simplfying the boot process nicely, initramfs allows appending additional images to the main boot image, and the kernel assembles them all into one filesystem in memory. This is great because it points to a way to support non-free kernel modules and firmware, which has been split out of the Debian kernels entirely in 2.6.11 -- ship the images separatly and let the user cat them onto their image if they need them.
There's still some details to work out, but I think it's all doable, and there will be benefits beyond supporting non-free stuff.