Well it is basically an almost-copy of Boost.Filesystem which you can use today, can you not?

Boost requires compiling libraries ahead of time and linking them in, so to do that on top of Qt would be asking a lot for very little gain. If filesystem was a header only library I don't think it would be as much of an issue.

I assume that in the long run Qt will relinquish this to standard libraries, so QFile will basically be a convenience wrapper around std::file integrated with Qt's concurrency model.