(All these pertain to WP X4; they may be fixed in later versions)
The ability to overline words, not just underline.
An outline numbering scheme that applies only to headings. Word and LibreOffice offer this, but in WP if I apply a heading style, the instant I try to number it, the heading reverts to the default text style. Likewise if I have numbered text and apply a heading style, the numbers disappears.
A document map that automatically updates. Currently, I have to press the 'refresh button. If I have refreshed the document map, then open a new document, the previous document's map is still visible.
Similarly, dynamic update of word count. When writing articles for magazines, a dynamic word count saves me a lot of time.
Built-in reference manager. LibreOffice and Word now have basic referencing features. Or perhaps Corel could write a plugin for Zotero? This could be a real killer feature for WP, more so than features like ebook publishing or importing of pdf documents neither of which are particularly well implemented as far as my experience goes.