pkgbase? We split base up into packages and deploy binary updates via our package manager, pkg(8), instead of with patches distributed via freebsd-update(8). We have a lot of build knobs that can make some parts optional, and some of those get turned into their own pkgs that end-users can simply not install (or remove) rather than having to manually extricate those or rebuild with some knobs set.

You can find a better (though slightly outdated) description here: https://wiki.freebsd.org/PkgBase