You want something faster than bash – write something faster than bash
with as expressive a syntax (and ideally the same syntax). Winning CPU
time by consuming packager time is not going to work.

This seems like it's begging the question. "The same syntax as bash" is just going to be bash. And if it's going to be bash, we should call that out as "bash," which is Step 0 for anything else.

Removing bashisms is a change, but it's not a huge change for shell snippets here and there. (Unlike other parts of the distribution that would probably have a lot of gettext substitution to deal with.) Yes, there are syntax changes occurring, but most of it's going to be more along the lines of "Please tweak these C++-style comments so we can use a C compiler" than anything else.

-jc