[jbrnh]

env and sh are both POSIX but AFAIK the path is not specified for either of them. If POSIX has an opinion on how you should start a script I would be happy for a link?

Bash in RHEL is in /usr/bin and /bin as /bin in symlinked to /usr/bin. I think it is equally unlikely that RHEL (Debian, SLES..) will will move either /bin/bash or /usr/bin/env as it would break a million scripts out there.

If we should migrate to FreeBSD while, for some reason, reusing linux oriented bash scripts, changing the path to /usr/local/bin/ would be the least of my headaches.

I agree that 'env' can make good sense if you don't know who/where/when your script is used. For internal projects, I don't really see the advantage.