It seems commonly assumed that Alduin was 'destined' to reappear on Mundus in 4E201, and fate ensured that his slayer, the Dovahkiin, was all set in place in Skyrim in order to appropriately defeat.

But is it plausible that it was the other way around? Alduin was just adrift in time with no set date for return, and it was the fortuitous proximity of the Dovahkiin and his/her dragon blood to the time wound that caused Alduin to fall out, for want of a better phrase. By this explanation, there's no reason why our Dovahkiin is particularly special - there could have been plenty of potential 'Dovahkiin, Slayer of Alduin's throughout history, but because they never happened to be near the time wound they didn't become the one.

The best argument I have against this idea is the prophecy for Alduin's return and all the conditions have just been fulfilled, then he's back. However, I suppose you could say it's like any prophecy: you can interpret it in many different ways, if Alduin had returned at a different time other events would have been used to explain the conditions.