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:
+ Make gnutls independent of the Certificate Manager (in order to support
 other x.509 certificate managers)
* Add callbacks to get SRP parameters (instead of a reading password file)
* Trace memory leaks in libgcrypt
* Drop dnsname extension
* Minimize footprint.
* Add support for certificates with DSS parameters
* Add more TLS extensions
* Audit the code (volunteers?)
* Add support for PKCS8 encrypted private keys
* OpenPGP certificate support
- Add Kerberos support

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