I like the idea of including cffi-grovel. I would very convenient to me if it were included.
The dependencies worry me. I certainly understand the desire to avoid duplication of code, but making dependencies makes it harder to install. For example, none of these three dependencies is present in Debian, yet cl-cffi is. I know you're not the Debian maintainer for cl-cffi, but how would this be managed? Difficulty of installation is a bigger barrier for those new to Lisp, and I expect that CFFI would be important for many newcomers who wish to continue to use software they used in the non-Lisp environment.
Liam