According to specified technical requirements, a commercial application must be self‑contained in a single directory (which I agree is a good requirement), and use
~/.config/<app-name> for its configuration data (good requirement too). However, Gsettings requires to have a schema file installed inside of some subdirectory of
$XDG_DATA_DIRS. Do I have to understand commercial applications can't make use of GSettings?
I've found another page, which seems to suggest requirements are not exactly that restrictive. The latter mention installation of an icon file in
/usr/share/icons/ and a desktop file in
/usr/share/applications/. If that's OK, may be that's OK too, to install a GSettings schema in
/usr/share/glib-2.0/schemas/? That would still be better to have confirmation. I feel the first mentioned link, lacks precisions.