Illegally grabbing thousands of hours of music to train a commercial model hardly qualifies as fair use. Any company you build upon that would be tainted.

For sustaining:

In addition, you'll need to keep an updated catalog of music to identify new songs against, and most uses of a service like shazam are to find names of songs people aren't familiar with, so that catalog needs to be very fresh.

That means you'll have to grab some sort of feed, and engage in large scale music piracy for commercial gain or have access to a library of songs from many disparate music providers, such as ascap.

Background noise:

there are literally hundreds of different background noise environments you need to train against. Dozens of common microphone configurations. Clipping, variations.

It's very much a problem where a proof of concept is neat but doesn't really get you anywhere.