I had an idea close to this when the new covid contact tracing tech was announced. However with it being P2P there are a few issues coming to mind:

- How to ensure privacy from man in the middle attacks? If your phone has to send data to other phones for them both to agree that there is a match, one would be able to abuse this to gather information on nearby people. I'm not well enough versed in cryptography to know if there is any solution like that for this.

- How do you make money from it? If you're building it purely for its own sake sure, but if you're trying to be a startup, then privacy side is not a killer feature for enough people to use it to make a dent but it is a massive engineering sink.