When I added hotkeys, the main idea was to support a mouse-less (keyboard only) system of game control. I wanted to add a shortcut for every button (even play card - this would be accessed by number 1 - 8). Hotkeys for webpages are standardized by W3C, but even so, each browser has different implementation. Most browsers have their own hotkeys which override hotkeys defined by webpage. Some browsers provide an alternative way to access hotkeys of a webpage, so this partially solves the conflict. Under these circumstances I am unable to implement hotkeys that would work for any browser the same way. Until this situation is solved by browser developers, I am unable to make any progress.
But as Progressor said, it's questionable if someone would even use such a feature even if it would be implementable, since using mouse is more comfortable.