No those alternative keymaps are not working for me either - as you say they load but don’t work.
I think the issue is that on the Fire TV the remote must present itself as a “keyboard” device, thus the keyboard tags in the xml file, however on OSMC it probably presents itself as a “remote” device since the keystrokes are passed to Kodi over a lirc socket. So in theory the tags would need changing to remote instead of keyboard, however when I tried that it still didn’t work! So a bit more investigation is needed…