SNI: Shiny or Scary New Idea?

I've known for awhile what my next novel will be. I refer to it as a Shiny New Idea, but really, it's an old idea that's recently been polished. My current project either doesn't include or doesn't focus on any of the subjects my SNI would, such as friendship, a two-girls-one-guy love triangle where it's (hopefully) not obvious which girl the guy should choose, Nova Scotia, musicians, and summer.

Of course, I don't know how the novel will turn out until I write it, but I know I can write about all the topics I listed. Aspects of the project scare me--like, uh, its lack of plot--but the subject matter doesn't. 

But recently, I had a dream which inspired me (I know, please stay with me.) I've never been inspired by a dream before, but when I woke up from that one--I honestly can't remember the dream at all--I thought, "What if I write a character who ___ ?" (I know, but this idea isn't fully fledged yet--and may never be--so the rest of this post will be ambiguous. This post isn't about the idea itself.) 

I toyed around with that idea for awhile, and tried to put it in the context of a story I abandoned last summer. It still wasn't working, so I forgot about it. Then, I listened to a song I hadn't heard in awhile, and I had to pause it after the first line because I was so struck by it, and the story it sparked in my head. Once I put the novel I abandoned, the idea from the dream, and the inspiration from the song together, I had something--not enough that I could write a practice query, or even eloquently describe it now, but enough for me to explore it. 

I'm a pantser, so what scares me the most about this idea isn't that I don't fully understand it yet, but that, unlike the SNI I discussed earlier, I don't know if I can write it. It's dark, and though my novels aren't purely fluff, they're not dark. That said, my novels do have some fluff, and anything that seems romantic in this new SNI would always have a borderline disturbing quality to it. Also, worldbuilding would be crucial in this novel (though it's still contemporary), and I am slightly terrible at worldbuilding (understatement of the year.) 

I like this idea, but I don't know if I'm the person to write it. I'm scared of it. I'd love to tell you that I'll be brave and try it after I finish my current project, but I don't know, I may not. I may stick to the safe idea--which I still like--and let this one sit for awhile. I don't know what I'll do.

And that's why I'd love to hear from anyone who has been in this situation. Have you ever had a Scary New Idea? What was it? Did you try it? Did it work? Let me know in the comments!