Trunk is not stable and is not recommended for a production site.
I just backported the support for Mediawiki XML files version 0.4 from trunk to branch 6.x. So it should be included in version 6.1.
So I suggest you wait for version 6.1 or start your site running branches/6.x which is much more stable than trunk (after 6.1 is released all the commits are reviewed before being added to branches/6.x).
Note that the only thing I did was to change the importer to accept Mediawiki XML file 0.4. I haven't check what have changed from version 0.4 and version 0.3 and I did only a very basic test importing a Wikipedia article XML file version 0.4. Some changes might affect the importer. Please let me know if you find any issue.