Currently internal eZ routes are imported in main ezpublish/config/routing.yml.
Internal routes can hence be deactivated, which is something we don't want.
Another thing is that custom REST routes are currently only identified by the %ezpublish_rest.path_prefix%, which is not very clean either.
A good solution would be to implement route loaders, having different types (for core, legacy and rest).
For REST, an ez_rest type would make custom REST routes easy to identify.