Yeah, consider this nothing more than Doctor Who speculation time once again, but I was thinking recently about the probable exit of current companions Amy and Rory Pond at the end of Series Six later this fall.
With only Matt Smith confirmed as returning for Series Seven, it seems likely that the Ponds are being written out of Doctor Who...at least until a potential return for the show's 50th anniversary in 2013. So while watching the Series Five episode "The Hungry Earth" again not too long ago, I wondered if we'll see the flip side of an encounter that takes place early on in the episode. If you recall, the story was set in the year 2020, ten years later from the time that Amy and Rory both began travelling in the TARDIS. The two see what is presumed to be their 2020 selves waving to them from a distance, seemingly revisiting the adventure their 2010 selves are now taking.
Since the Doctor has been shown in recent years as being a sentimental old sort, and showrunner Steven Moffat absolutely adores to play around with timey-wimey storytelling, I've been wondering if these 2020 versions of Amy and Rory will actually turn out to be the Series Six Amy and Rory waving goodbye to their earlier "Hungry Earth" selves. This, of course, means we'll see this same scene again, but this time from the other perspective of Series Six Amy and Rory.
Just a thought of mine that may not pay off, I know, but if Moffat deliberately set up Amy and Rory's eventual exit in advance, it would certainly be consistent with his handling of River Song and the mysterious Big Bad manipulating events from behind the scenes over the course of multiple seasons. In any case, I heartily recommend stocking up on tissues for the Series Six finale...