Jet-fu's vanilla kernel will be as modular as possible to allow it to be as small as possible.
For preinstall, the livecd boots, the kernel does its magical hardware detection (I still have to delve more into kernel hardware detection, so it's still magical ;) ). When the installer is run, it'll run lsmod, pull the output, clean it up so just the module names are written to modules.conf, write modules.conf. Then use modules.conf to install just the modules that are actually needed.
For post-install, I actually have some pseudocode. That script will be called modinst, and it'll be used in place of modprobe (more specifically, insmod). So when modinst foo_mod is run:
wget -nvc ftp://server.for.mod/foo_mod
It triggers a script to grab module from server and put it into the modules dir and then run modprobe to install it.
So far this looks good to me, I welcome comments on whether this actually sounds like it'll do what i want it to do, or improvements.