the fully keyboard driven website is difficult to achieve, in some part because of accessibility tools, first off every OS has their own hotkeys and keyboard shortcuts, generally with some explicit modifier, the reason for modifiers is that it is good to have a key you push in coordination with some other key to force something to happen outside the functionality of whatever thing you are currently interacting with.
Second browsers often have their own hotkey combinations. Same things apply.
Third screenreaders have their own hotkey combinations that make the screenreader do something.
fourth parts of your site probably have their own specific functionality for key presses, like this text box I am writing in right now.
fifth people with accessibility issues and just anybody with some technical needs or abilities may have set their own global hotkeys in their particular OS.
sixth some keyboards might not have the keys you think of as really clever modifier keys.
So, if you really wanted to get around problems of potential hotkey collisions you should provide a default hotkey set that users can edit and override , and that is why I always get accused of over-complicating everything I do.