This seems like a substantial task if we want it to be cross-platform at all. Below are some details on how Cocoa is configured with system-wide key bindings. https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/EventOverview/TextDefaultsBindings/TextDefaultsBindings.html
<rdar://problem/23690419>
Respecting this in WebKit was super-challenging; I expect this will be hard to do. Being cross-platform isn’t the hard part; it’s easy to make a hard-coded version for the non-Apple platforms that matches the approach those platforms take to such things, since a system bindings file is a sort of unusual feature. The hard part is finding a way to pipe keyboard input through the public Cocoa APIs to figure out what editing operation to perform. There’s some internal interface that is a bit more flexible but even relying on that probably wouldn’t be a big help. Probably not worth the effort :(