My suggestion for OO 5.0 would be improvement and extension of OO's Navigator. 

If one refers to Bugzilla 3959 at 
https://issues.apache.org/ooo/show_bug.cgi?id=3959 
one can see that there is a long standing call for OO to have an Outlining system similar to MS Word. 

Such an outliner might closely integrate with the functionality of a Writer's Organiser, which allows an author write chunks of his text and then dynamically rearrange them; in addition, such Writer's Organisers also permit tracking each chunk by the persons, locations, things, times involved.

I instance two good working examples of such Organisers (opensource):

Plume Creator, by Cyril Jacquet, at
http://www.plume-creator.eu/site/index.php/en/
written in C++

and

oStoryBook, overseen by favdb31 (sorry - I've lost the link to his full name), at
https://sourceforge.net/p/ostorybook/discussion/?source=navbar
a revival of StoryBook (now discontinued), written in Java.

Both of these are currently undergoing revision - oStoryBook in particular to allow use of an external editor.

The extension of the Navigator might also support the extended OpenDocument MetaData functions (v 1.2? - Rob?) 

Such a Writer's Organiser would fill a useful gap for authors, many of whom use Scrivener (commercial). It also might parallel a commercial product for Microsoft Word (I only know of this from looking at the site) of Writing Word Outliner at
http://www.writingoutliner.com/.

The Calligra project has under development (slowly) Calligra Author, which does not yet offer the full functionality of either of the above.