Wasn't the Donkey wheel the thing that Jacob's brother was building to get off the island? Did Jacob finish the project for his brother?
Yes, it's unclear who finished it though. If I recall, it was actually Esau (Man In Black) who advised John to turn the wheel a few seasons back, albeit disguised as Jack's Dad. You have to think at least Jacob knew about it...
I saw another ad last night for the finale that clearly showed the wheel being turned, so I'm thinking we'll see it again.