Hear me out!
A mod in GTA 5 that allows you to simulate random disasters, like a whole plethora of them. With the optional feature to have the world of San Andreas interact around the disasters.
The mod could have disasters ranging from earthquakes, meteor strikes, tsunamis, tornadoes, floods, terrorist attacks, zombie outbreaks, volcanic eruptions, foreign military invasions, nuclear warhead attacks, an all-out gang war, forest or city fires, statewide riots, ice age, any disaster you can come up with.
Just really cool but dangerous events that can make playing the game more fun.
The disasters could start with a public announcement on your screen, a siren playing, or a news report.
And with a configurable ini file to configure the intervals of the time a disaster approaches, and the percentage chance of the type of disaster it will be.
If possible it would be really cool to see the LSPD or any government forces reacting to the disasters, like the police or military actively seeking out the zombies or the terrorists, news helicopters covering the disasters, firefighters coming in to help people from fires, medical personnel tending to the injured, SWAT/NOOSE holding off the riot that is taking place.
Another idea is to implement an optional feature for the player itself to be able to make a change in these events, such as defeating the terrorists, saving civilians in a location where they are trapped, finding the cure for the zombie virus, either helping the police or the rioting mob, helping firefighters extinguish fires, riding a boat to rescue castaways after a devastating flood or tsunami.
Regarding the technical side, I think this hypothetical mod needs a fair investment of time in order to create it.
It has a lot of features and the games engine could limit it making a lot of the features unable to be implemented.
Even if most of all these cool ideas can't be modded to be in the game, I bet the community which has a lot of great modders alike is able to at least create most of this into a reality.
In short, it'd be cool to have an all-in-one mod with a variety of disasters and the world interacting around it.