If I remember rightly, in Chromebooks the "search key" (which is located where CapsLock would be on a normal keyboard) is really the "windows" key (or "super" key). Chromebooks don't have windows keys in the usual place, and so Google seem to have decided to replace CapsLock with the windows key, and then redefine the windows key in the OS to perform the custom search operation.
I'd say this means your best bet would be to remap the meaning of windows/super key in the xkb files if you want it to become backspace.
On the one hand, it's good that google have realized there are better uses for CapsLock, but taking away a modifier key is a fail in my view.
Last edited by stevep99 (20-Dec-2016 11:54:35)