I added a GIO backend to master, but I had to disable it because it is broken in a serious way:  it doesn't work with writing metadata with taglib# because the write streams it can open cannot also be read from.

There is a fix in recent GIO apparently for a stream that can do that, and sde has told me he's already done some work to get that into the gio# binding, though I'm not aware of the current status.