This post is more than 2 years old.
I say "possible" because I haven't read it myself, but a reader pointed me to this book by Eric Bidelman, "Using the HTML5 Filesystem API". It is nearly four years old, but the reader said it helped him, and I know folks are desperate for more help with the FileSystem so I thought I'd pass on the recommendation. There is a free chapter you can sample if you want to check before you buy it. If any of my readers get this, or have read it, I'd love to hear your thoughts below.