It's an amazing idea. We tried to do something like this with colleagues. We gathered together and exchanged different ideas. It was a bit difficult at first, but then we tried brainstorming techniques. It was a real skill booster One of the best tools for a literature group. You have a very short period of time to solve a task, so your brain starts working whether it wants to or not. Anyway, it was a positive experience.
I think the 'proper' term for having too many ideas to ever write is called a 'plot bunny'. As for how to attract people to it...the only way I tend to hear about groups is when they're doing contests & the lit staff advertises it. That sort of community interaction might get you a few followers.
Why not just make it about writing prompts, or what's often called plunnies or plot bunnies. Folks that being writers post plunnies they don't want to write for, but they have the idea. Someone picks it up and rolls with it if they want too. Could work. Dunno how many would be interested in it though.
Not quite sure, what this thread is supposed to be, in the title, you say you need ideas, but in the post, you say this is an idea dump. I'm not quite sure, if this fits, but maybe this is what you imagine to be posted here: Scrap Collection