So I have a couple of events in mind that'd I'd like to see Xsyon do.
The day of/before the final wipe: Doomsday.
Just invade the world with mutants/zombies, crazy bears, giant deers and just be crazily infested with different mobs.
Second event- after about a week of the final wipe send waves of mobs at encampments and give us a reason to defend ourselves. These mobs (if possible) could even steal materials and other such things out of our baskets and things that are just laying about.
You could do the second event periodically and call it horde(or something). Give us a reason to defend our homes.