The init-scripts (and other shell scripts) in Gentoo use /bin/bash, instead of /bin/sh.
As Gentoo is supposed to be about customization, the Bourne shell used by the system should be changeable. Currently you have to have bash, even if you don't want to.
Also the system's default Bourne shell (/bin/sh) should, in my opinion, be a static executable. Just in case...
Steps to Reproduce:
it may bear some thinking about with respect to /bin/sh versus /bin/bash but it's not high priority, unless you can come up with equivalent portable functionality for us.
as for static shell, we provide app-shells/sash
The rc system tends to use a lot of bash-specific functions. Many other tools -- including Portage and ebuilds -- also require bash and make use of bash internals not available in a POSIX /bin/sh. I highly doubt it will ever be possible to install Gentoo without bash; it would require reworking just about everything.
Obviously, you can change the default shell for users to whatever you like.