Nacl was designed by cryptographers for exactly this problem.
I'd welcome some full-fledged libgpg that would reliably implement gpg the executable's functionality, similar to e.g. libcurl vs. the curl executable.
For the record, I'm a Signal user and advocate.
We will undoubtedly have to integrate and access libraries like NaCl. But we should do so in keeping with best practices recommended by cryptographers (e.g. through NaCl's documentation), not by layering an arbitrary scheme on top.