[chrismsnz]

Yes, root's shell should be one provided by the distribution's base install.

I think the biggest worry is that if you need to do something like boot into single user mode for an emergency recovery, and /usr or /usr/local (with root's shell in it) is on a different or unmountable partition then you will not be able to do anything.

[knob]

Additionally, if you upgrade your shell, or something gets borked, then... you now don't have a shell.

[allanjude]

This is one of the reasons for the existence of the 'toor' user, which still uses the default shell