Indeed - for all folks disillusioned by systemd, Gentoo is a source based rolling release distro whose fundamental tenet is choice - so it shouldn't be a surprise that it is possible to use alternate init systems on Gentoo, in fact Gentoo liveCD/handbook defaults to OpenRC while providing the choice to run other init systems (I run systemd with a somewhat complicated RAID setup with no problems).
As a fellow gentoo-user, I am extremely happy with it.... until it's kernel upgrade time. I've managed to forget the set of flags needed to make my system work as desired. So it's a pretty painful process.
run `zcat /proc/config.gz > ~/kernelconfig` (i believe that's the right filename for the average Gentoo kernel; haven't booted Gentoo in a long time) and you'll end up with a full list of all the options you chose for your currently running kernel.
This shows all the config options. Options change from kernel to kernel so doing a simple diff does not always reveal the user's intentional config changes. Otherwise gentoo is painless.. in the long term.
I never used genkernel. When I compile a new kernel version I just eselect it, cd into /usr/src/linux, "zcat /proc/config.gz > .config; make oldconfig" and go through the new options manually. I also have scripts for the modules/kernel installation and the recompilation of packages with kernel modules.
