This sounds like a really cool idea. I don't know how I feel about editing posts over and over, though. That sounds tedious. Moving through the entire plot sounds much more plausible, but I would imagine you would need a pretty short plot in order make this work well. A short plot that can still be interesting. Maybe go back in time in chunks instead of all the way to the beginning. For example, once you get to the end, maybe the characters would think going back in time only a few hours would render their desired end. Then they may go further and further back. Maybe they won't go in any order, but choose completely random points in the plot to return to.