I didn't have enough time to read through this whole post, but from what I've seen, most people seem to be trying to pinpoint an exact historical event for the song to be about...
My personal opinion is that it's much more general of a "revolution" song
If anyone is familiar with Carl Orff's Carmina Burana, and more specifically O Fortuna, and the whole idea of The Wheel of Fortune, then you might already understand what I'm talking about. The Wheel of Fortune depicted the rise and fall of kingdoms, from the revolutionary stage (spring), through the ruling stage (summer), into the declining stage (autumn), ending with the defeated stage (winter). Orff's Carmina Burana follows the same cycle, starting in winter and following around through the seasons until it returns to winter once more.
Obviously Viva la Vida is not in the same format or anything like that, but I think the general sense of the fact that Viva la Vida, or "Long live life," as I think it's supposed to be translated (I know the Spanish translation is simply Live the life), is paired with "Death and all His Friends" in the album title is very significant for such an interpretation. The Wheel of Fortune is also frequently used as a metaphor for a person's life.
Now, all this might just be crazy rambling without much of a point, but what I'm really trying to say is that there is: 1) too much ambiguity in the lyrics themselves to justify a single historical or religious incident, 2) too much symbolism in the words themselves that pull in too many directions, and 3) that there are enough theories that seem plausible that one single answer is not enough to fill all the cups...
I guess the only real way to settle this dispute is for Chris Martin to tell us for sure...