> What actually happened to quvi?
Good question, I didn't keep track of its development. Your best option would be asking developers if they are planning to work on it further or not.
> By the way, FFmpeg has support for the 0.4 branch of libquvi
Same as mpv I think. You can play Youtube videos with it directly:
mpv "$url"
Which is kind of fun, since you can do tons of things that aren't available in the browser player - looping, playing only portions of the video and all other things which mpv can do.