ECDSA is supported since February 10, 2016 (#260)

Let's Encrypt will however sign all ECDSA certs with an RSA intermediate certificate.
https://letsencrypt.org/upcoming-features/

docs/ecc.md

 ### Elliptic Curve Cryptography (ECC)
 
 This script also supports certificates with Elliptic Curve public keys!
-Be aware that at the moment this is not available on the production servers from letsencrypt.
-Please read https://community.letsencrypt.org/t/ecdsa-testing-on-staging/8809/ for the current state of ECC support.
+Simply set the `KEY_ALGO` variable in one of the config files.