quoted

Surely that is just a new keymap ?

No. That would mean a lot of keymapSSS. Doing it the keymap way

Why - its an  algorithmic question about how to edit them - remember you
can edit keymaps in programs at runtime and live.

This really is a problem that is orthogonal to keymaps: I'm here talking
about _physical_ keys remapping, not remapping what is printed on them
(which is done after that).

Ok so this is analogous to the X key remapping. In which case a notifier
seems as sane as any other way to perform the action if you want it to be
an add on loadable feature.