I would like to repost a comment from reddit[1] that makes some good points: "That title is pretty laughable. Enterprise E-Mail Encryption solutions do NOT use gnupg, and most enterprise customers do not even use openpgp, they use X.509/SMIME. I know the world top 10 server side enterprise e-mail encryption solutions and the majority uses java with either bouncycastle or ajak encryption, for PGP or openssl/bouncycast…
The request was refused [1] with ridiculous arguments [1] about PKCS#11 not being "needed in free software world".
After that, I started playing with S/MIME and found out it was much more user-friendly than GPG. (After the initial setup.)
[1] Here you can find links to relevant threads: http://zvrba.net/software/gpg_pkcs11.html