It's been over 2 years since I raised this issue the first time. The specification has not been http://www.w3.org/TR/file-writer-api/ updated in a year and it states that:
Work on this document has been discontinued and it should not be referenced > or used as a basis for implementation. The problem of how to: - Asynchronously write a large file (FileSaver & co.) - Right click save-as - Overwrite (simple save) Is still not solved, and nobody tries to solve it. I find the status, progress and abandonment of the topic unacceptable. A variety of productivity applications (google docs, verold studio, fabric engine, goo engine, etc.) exist now on the web (and more are added daily), and they're all having the same problem, saving files conveniently for a user is not possible. It should be possible, but it isn't for the failure to specify and implement any kind of solution to it.