Can you do this with any piece of writing on Etherpad?
Anything you write with it now you will be able to play back like this soon. Etherpad is already saving all the keystrokes. They just haven't released the player yet. (This is a one-off prototype.)
This site shows how some fairly good illustrations are drawn (brushstroke playback). Unfortunately, not all drawings can be animated and the ability to search for playback-capable drawings is limited:
It would be interesting to have the timestamp data (if it is recorded) of the keystrokes (adjusted to author's timezone - privacy withstanding) so you can see a clock/calendar [day|night icon] when the author wrote it (was it 3am in the morning? did they put it aside for a couple hours or was it a period of days?).
However, it should be somewhere hidden and available only if people really want to be able to replay. Else it is going to be an over kill on their servers.
Anything you write with it now you will be able to play back like this soon. Etherpad is already saving all the keystrokes. They just haven't released the player yet. (This is a one-off prototype.)