To me it seems obvious that you can write any application using any Turin-complete language. So the question seems more like "how convenient would it be to writ

To me it seems obvious that you can write any application using any Turin-complete language. So the question seems more like "how convenient would it be to write a kernel or a game using Julia and with which performance impact?" For games, it will highly depends what kind of game, of course. Assuming cutting-edge 3d-graphic intensive video-game, it will be probably not be your language of choice, especially regarding available out of the box libraries. For implementing Tetris, I guess you make it in any language for sufficient performance. :)