For a collaborative prompt, I think it would be more fun if it is "by the pants," and not plotted out. Also, to work off the previous chapter. Wildthing and I did something like that in the past, reading the previous chapter, then building a next one is fun to do.. or half a chapter. It was interesting to read the transitions in writing styles.
Either way, I'd be interested depending on theme/prompt. With that said, with these prompts nothing is coming to mind for me, but I tend to have to sit and think about it for a bit before something does.
Right now Prompt: 299B is the one I'm leaning towards, if I was to do one.