Instead of compiling a single new kernel module (or downloading it prebuilt from an apt repo or a PPA) and kicking it in with modprobe, we now need to obtain the sources for the whole kernel, apply the patches, configure, build, and deploy. Sure Debian/Ubuntu has that partially automatized but it's still a pain.
At least I'll wait for stock 2.6.38 on Ubuntu and cross my fingers they put this patch in.
: I Am Not A Kernel Hacker
Obviously, any change to the default behavior is going to require building a new kernel.
There may be good reasons for completely plugable schedulers, but this is not one of them.