Right now it's not possible to schedule publishing of expired pages. A walkaround is to remove the expiration and change the publish date to the future date. That will make the page published for a short moment (until you save the future publish date) though which is not desirable. I would like to see better support for this.
Can't you just create a draft from the expired version and schedule the draft for publishing, or does that mess up publishing dates or something you don't want messed up?
That was what I was hoping for but unfortunately the draft gets the same expired status when trying to schedule/publish.