Write the press release before the code (or anything else)
That’s exactly the point. If you think about the PR that will eventually be written for the release, it will help you and the team focus on what is sell able and really matters.
Think like a writer. Come up with a main point (feature or benefit) and perhaps a couple of supporting points and write it up. This will end up exciting the team (including executive management) about the project far more than a feature list spreadsheet of 273 rows that lists everything in priority order. Of course, you need that too, but having the pitch down will help everyone align on the priorities.
(Disclaimer: I ‘stole’ this one from a CEO who kept asking for the PR in planning sessions for this very reason)