I've seen this done 20 years ago before flash in a java applet. What's your point?

Java applets where released in 1995, flash was released in 1996.

Clearly missing the point.

The sad part is you really still can't do this in HTML5, not if you want it to run on the most popular smartphone platform (Android).

Give it about a month and Chrome for Android will provide web audio API support. It's currently in chrome for android beta

Our web app that plays audio in sync on multiple devices works in iOS, Chrome (non mobile) & Firefox Aurora. Were eagerly awaiting for the newest Chrome for Android to drop.

That's good news! What I really want though is to run it inside a WebView rather than just a mobile web app. I feel this gives more control over the experience, screen real estate, monetization options, and deeper integration with the device's hardware features.

Run it in Firefox on Android. Android default browser is junk.

Wouldn't it work on firefox for android?

It would, but the default browser is what WebViews are based on. So you give up a lot of power and flexibility by just targeting Firefox or Chrome for Android.

Android isn't the most popular smartphone platform. It's the most popular phone platform.