Actual the full functionality + more will be available within the 1.5 (or later). I've contacts with Johan / Andrew and Wilco about this integration and have patched the 1.5 already. You can add additional fields, etc.. see http://www.alledia.com/blog/joomla-1.5/great-seo-improvements-in-joomla-1.5/
for more info about the functionality.
The only problem is to get it integrated. The changes I've made have impact on different core files and these should be talked through with the core members like Andrew. Only it seems difficult to get in contact with each other ...
We support the fact that this functionality should be available within the core of Joomla
The current status is that it will not be included within the 1.5 release. But I've the same issue with a project where these improvements should be available. When the final release of 1.5 becomes available I will patch the 1.5 release again.