Shorter novels appear to be the wave of the future. I think there will always be a place for the massive 17 book novel series, but shorter works have a couple of advantages:

1. You can take more risks with events that forever change the world. If you write a huge novel series and a massive world-changing event happens every book, the reader will get tired of it. However, if you write several shorter works in different worlds and each of them has a different and unique world shattering event, the reader may not tire of it.

2. As you said, more output. More books = more chances for readers / more sales.