You can assign a previously unused keyboard shortcut to the File menu : Export To > Word… menu item and that is it. This does not automatically complete the export process though.
When you type that keyboard shortcut, you will still encounter the drop down sheet with Word preselected, and you must press enter to get past the Next… button. The following sheet is the Export Save panel that is already populated by the current Pages document name with the Word .docx extension. If you are happy with the filename, and the current save location, you can also press enter here too.
Before you perform the following to assign a keyboard shortcut to Pages, I strongly encourage you to initially review the existing Keyboard Shortcuts assigned to Pages by Apple. That is located in the Help menu : Keyboard Shortcuts > Pages for Mac keyboard shortcuts, or this link to the same source in your browser. You don't want to collide with existing shortcuts.
In System Preferences : Keyboard panel : Shortcuts : App Shortcuts:
- Press the + button to add a new application shortcut
- From the [All Applications ↕︎] selector, choose Pages
- Menu Title: Word… (that is an ellipsis which is option+; on U.S. Keyboard)
- Keyboard Shortcut: control-W (press control key+ W)
- Click Add
- Quit System Preferences panel
You have now added ^W to the File menu : Export To > : Word menu item. I used ^W shortcut as an example without checking the keyboard shortcuts because I will now remove it from my Pages application in the previous App Shortcuts panel.