EDIT: In fact, scatch all what I wrote before. I shall explain it better:
The purpose of our mod is to simulate the evolution of World religions. To this end, specifying the nature of the apocalypse (even if it is just the belief in such things) is not something we would want to do in a literal sense.
As your religion becomes more and more pious, more and more can (that's "can", not "will" for anyone worried about this mod being about religion as a force for intolerance / war) previous doctrines you have picked (perhaps with the best of intentions) bite you on the backside as your more fundamentalist followers start issuing demands. Perhaps some of your early doctrines in combination have inspired your followers with the belief in an End of Days. You possibly could have predicted this when you picked them but, heck, those perks were awfully tempting and now, unfortunately, your followers have decided to take them as literal... oh dear, they've demanded that you wage war on the spaceship building heathens. Whoops.
This is the sort of mechanism we find much more interesting and rewarding than a literal "pick your apocalypse" system. That said, we welcome anyone who makes a mod mod of ours.