I don't think that the server is in charge of priorisation here. The server can do it, but there is no reason to push this responsibility onto the server when the browser can do it much better (for example the server can't know what's in the viewport).
I expect this will be quickly sorted out by more mature HTTP/2 implementations in browsers. Downloading every image at once is obviously a bad idea, and I expect such naive behaviour will soon be replaced by decent heuristics (even just downloading eight resources at once should be better in nearly all cases)
I expect this will be quickly sorted out by more mature HTTP/2 implementations in browsers. Downloading every image at once is obviously a bad idea, and I expect such naive behaviour will soon be replaced by decent heuristics (even just downloading eight resources at once should be better in nearly all cases)