@Cass
Did you want this to be a solo effort or group?
I usually steer into Solo territory, I'll try to make an exception with this project. My current plan is to, sometime in the future, code a script that acts like a framework where adding self-contained scenarios would be easy. Then add basic scenarios and set up a github or something, so people can contribute.
Pretty nice suggestions, I've specially liked
peds washing cars / bikes / bicycles in front of their homes
peds fishing at the pier
because these are easy to do (script-wise) and would provide totally new content to the game. If there's an animation/scenario for it, both would be very simple to add.
Shark attacks
That would even be possible without scripting, setting up ped relationships and finetuning shark spawns. I think @mkeezay30 's GTA Realism features this?
hunting parties in the woods hunting for and shooting at bucks, rabbits, whatever.
That would really add "life" to the countryside.
groups of mexicans waiting to be picked up by a truck to work in construction;
This one gave me an idea. What about the contrary? Force peds who are working to stop working and leave the place at late evening or so?
It also reminded me that I tried to make working bus stops sometime ago, they worked well but had problems with bus alignment