Don't you think it could be a good idea, that Ext team provide a SVN (or CVS) repository for GXT extension ?
Then when Ext team think an extension is good enough, then commiter rights (on GXT-Ux only) could be allowed. I could be useful as there will have a central repository and then any commiter will be able to fix an issue (even if he's not the creator).
Ext team could also provide a single library for GXT extension. Of course those extensions have to use the same licence (LGPL for example).
And why not a GXT-Ux showcase ? You know it's not easy to see at the same time all extensions provided and it could be very useful to see them in action !