If you want to contribute (implement something from the current list, or
anything), contact the developer's mailing list (gnutls-dev@lists.gnupg.org),
in order to avoid having people working on the same thing. 

Current list:
* Try to use _gnutls_hash_fast() and _gnutls_hmac_fast() where
  possible. Especially when hashing/hmacing records. This would
  allow direct usage of CPU or chip acceleration, which do not
  typically allow multiple hashes.
* Add certificate image support (see RFC3709, RFC6170)
* Perform signature calculation in PKCS #11 using not plain
  RSA but rather the combination of RSA-SHA256, RSA-SHA1 etc.
  That will allow the usage of more secure tokens that do not
  allow plain RSA.
* Allow setting a PKCS #11 module to gnutls_x509_trust_list_t, to verify 
  against, similarly to NSS way.
* Support replacing individual algorithms via a PKCS #11 module -
  maybe use p11-kit for that.
* Support PKCS#8 AES and DES-MD5 (tests/enc3pkcs8.pem) encrypted keys.
* Implement TLS-PSK with PKCS #11.
* Add support for generating empty CRLs
* Document the format for the supported DN attributes.
* Audit the code
- Add function to extract the signers of an openpgp key. Should
  be similar to gnutls_x509_crt_get_dn_oid().
- Add function to verify an openpgp key against a plain key.
- Clean up name space of helper functions in library (memmem,
   firstElement, bit_mask, ...) for platforms that libtool's
   -export-symbols-regex doesn't work.
- Add Kerberos ciphersuites
- Certificate chain validation improvements:
  - Implement "correct" DN comparison (instead of memcmp).
  - Support critical key usage KeyCertSign and cRLSign.
  - Support path length constraints.
- RFC 3280 compliant certificate path validation.
- Add progress handler gnutls_{dh,rsa}_params_generate2, to allow
  application to give progress feedback to user.
- Chain verifications.
  - Check path length constraints.
  - Check keyCertSign key usages.
  - Reject extensions in v1 certificates.
- Exhaustive test suite, using NIST's PKI Test vectors,
  see http://csrc.nist.gov/pki/testing/x509paths_old.html
  and http://csrc.nist.gov/pki/testing/x509paths.html
- Make gnutls-cli-debug exit with better error messages if the
  handshake fails, rather than saying that the server doesn't support
  TLS.
- Make gnutls_certificate_get_ours return a zero-terminated array (or
  add a new API that return the size of the array).

(+) Means high priority 
(*) Means medium priority
(-) Means low priority (ie. nobody is interested to develop that)