This layout does not exist and we will never provide it.
However, having it in the XML file means it will show up in GUI configuration mechansism that parse the XML file directly (instead of using libxbkcommon's libxkbregistry).
Our rulesets fall back to the file "symbols/layout", section "variant" for any layout(variant) that's not explicitly covered. This enables users to create a symbols/custom file with their layout and have it available.
As there are no variants, the GUI tools will only be able to use the default section. Commandline tools can use variants as well.
This is papering over the whole issue only, but it does provide for some convenience. It will still require adding a file in /usr/share in most cases, but since we do not provide this file, it will be safe from being overwritten.
Fixes #257 (closed)
Note: one major drawback here: selecting this when there is no symbols/custom file may leave the user with a nonworking keyboard. Depends on the situation whether that is a problem, any runtime configuration (e.g. GNOME) shouldn't be an issue because you'll just end up with the server default (US). Putting this in an xorg.conf snippet however... probably not good.