First 50% implemented

v6 will also be able to export tree structures for the main content types.

There's a lot of work that can be done to improve things here.
1) Instead of exporting member ID's, export usernames
2) Merge in sources_custom/relations.php into our future upgraded content_meta_aware API (and hopefully the meta stuff in modules too - as modules should not define data schema). Each hook should be able to list table fields dependant on it's IDs. Any key entities will of course have to have a content_meta_aware hook (E.g. banner types, banners, topic polls, cedi posts, even menu items).
3) Using the dependency references, the XML exporter should be able to computer automatically what order to export in.
4) In addition to the permissions/seo-meta stuff already done there is: attachments (not yet defined in meta_content_aware hooks), awards (ditto), tracking (ditto), ratings, trackbacks, comment topics/reviews, member level permissions (msp, member_category_access), url monikers, point store permissions

Ideally we want really good staging support, where we can pick an item of content and click for it to be exported from one site, imported directly into another. And to be able to see when something is not in sync, and tables of things not in sync.
This is a huge undertaking though.

Also handling of custom fields.

Optional embedding of binary data, rather than only referencing stuff via URLs.

Custom fields partly implemented for Resource-Fs now.

Also handling of privacy settings.

Implemented, but as Resource-fs. The old XML import/export is getting dumped in favour of this vastly superior technology.