The possibilty to create custom content types. Choose the fields and fieldtypes they should have. The works.

A built in forms component will be very useful and would increase more possibilities by integrating in to the core

mutisite support in joomla.

Create a system for Joomla to manage site backups and restores. Explore the ability to also allow backup/restore for specific extensions or site sections.

o Build a system to support content versioning.
o Allow for compare and restore revisions.

Joomla Content Editor should be part of the core. TinyMCE is too feature poor of an editor and the media manager capabilites are much better than the existing one in Joomla core.

The possibility to translate everything (articles, menus, modules etc.) into different languages without the need of a 3rd party component.

o Improve various interfaces to be more usable on mobile devices.
o Build and expand upon Web service availability for use in external applications and devices.

I think that should be an advanced membership system.

Create an ability for a Joomla install to manage both a live and staging site where changes can be tested on a staging site and then pushed to the live site when appropriate.

SEF articles without the article/content id numbers in them. Similar to what Gallery Project has achieved.

Implement a tagging system available for content. Use the search index as a common location for content to be tagged.

Implement a commenting system available for content. Use the search index as a common location for content for commenting.

After installing Joomla everyone have to enter into www.site.com/administrator

for more security reason if should be grate to have an option during the installation to change /administration name it will be one of the grate function fro joomla core.

Reading and developing on Nooku Framework lately, integrating this framework to the core or at least as part of the standard components will boost joomla extension development.

As a matter of fact, adding nooku architecture to Joomla will improve and separate core development from extension.

I just became a fan of nooku development, so you should check its features. www.nooku.org

Allow site users to upload an image file to be associated with their profile. The image could then be displayed along with any site posts and/or comments.

This is a sorely missing feature for Joomla which I hope to see added in a near term release (version 1.7 or 1.8).

As Joomla and community extensions have grown and matured over the last 5 years, the admin UI needs to allow for the way the workflow and features have changed.

Option to easily add new user fields to user profile and manage user profile fields, something similar to the following image http://www.protechsystems.us/stuff/joomla/userfields_management.png

I will sponsor this feature up to $500, only if approved to be added to the core.