PostgreSQL is a non-commercial, all volunteer, free software project, and as such there is no formal list of feature requirements required for development. We really do follow the mantra of letting developers scratch their own itches.
The next release of PostgreSQL is planned to be the 8.3 release. As of April 1, 2007, the code for 8.3 is in feature freeze. All patches have been submitted for review and application. Patches submitted after this date will be held for a later version. The remaining rough timeline for the development of 8.3 is:
Please be aware that these dates are subject to change, though we will try our best to adhere to them as possible.
While there are no formal requirements for each PostgreSQL release, there are several places you can look to find out more information on upcoming features: