Getting into YC isn't the goal here... having a successful company/product is. I would try to just build something that solves a pain point for you. If you want to prove yourself based on what you can build in 72 hours, then pick something and do it[1]. That will get you more consideration than something like this.

[1] But, I'm not a fan of "look what we built in 72 hours" types of projects, so you may want to just try to build your product.