What exactly does this mean? How does a libc "support" a shell? I thought it was the other way around. Clearly tons (all?) of shells already run on glibc systems. Is this something that's only relevant for embedded systems?
Speaking as somebody who ports stuff to OpenBSD, it's a surprisingly common assumption in Linux programs that the standard shell is bash, when in fact it's not necessarily present on any other Unix. (sh, the bourne shell, is the default.)
While this sounds nitpicky, it's quite annoying to have problems testing a program because every single test case script has #!/usr/bin/bash hardcoded at the top. If it's using bash-specific extensions for scripting, that's understandable, but that's seldom the case.
Are you sure? Bash-style functions and arithmetic subshells are pretty common. As long as they don't label the script with the Bourne interpretar (/bin/sh) then Bash scripting is fine.