The API looks like it's designed for 3D games. For 2D games I'm not clear what the benefit is. You can already go in to fullscreen mode to prevent the mouse cursor leaving the window. There are downsides too: if you hide the real cursor and display it in-game, it has a higher latency so will feel laggier, so it's better to simply change the real cursor with one of the existing actions. Additionally for security reasons you can't just claim pointer lock right off the bat, you have to gain permission for it in a user gesture. It then makes it harder to close the game or multitask, since you are locked inside the game until you exit pointer lock, which I think is slightly obnoxious for casual gaming, especially in a browser.