I know it was said that it was optional to have these Mega Events happen, but will we be able to control the frequency? Example:

low frequency: Occurs once maybe twice (for the REALLY long games)
medium frequency: three to five times per game depending upon length
high frequency: seven to ten per game depending upon length

Those are, of course, just play numbers, and they should really be based upon the length of game (i.e. you could have ten mega events even on low frequency, but the game would have to be in it's 10000th turn to even get that close).

I just think it would be cool to allow people who want things a little crazy to be able to adjust that craziness depending on their tastes.