Wow, can't wait for this.

4-5 years ago, for my first startup idea, I actually spent a few months and built a client that will scan your complete MP3 library, extract and normalize ID3 tags, and sync with a web frontend.

The frontend lets you control and listen to your library in real time, and also multiplex your stream to as many listeners as you want. You could also browse and control your full music library through this.

Relevant news.yc thread from 1631 days ago: http://news.ycombinator.com/item?id=8753