You can use MIDI to make music in your web browser, and that's going to open up a lot of new possibilities.
But it isn't just about the music. There's such a huge range of MIDI controllers available that the web browser just became a perfectly viable platform for very basic embedded systems. One major, important trend in music software is external controllers which completely replace the computer as a user interface.
With the Traktor S2, released about four years ago, you didn't need to look at your computer very much:
With the Traktor S8, you don't need to look at your computer at all:
By contrast, here's somebody using MIDI controllers with loopjs.com to make music in the browser:
They're looking at their computer while they do it. But they won't have to for very much longer. Web companies will discover the same thing that musical instrument manufacturers have learned. And computers are shrinking rapidly.