What exactly should the enhancement be?

Assess across similar projects and perhaps put a poll out, to determine if the config/sync directory should be config/default (meshing with the sites/ directory for potential multisite usage) or something else.

Similarly, but separately, determine if contrib modules and themes should be modules/contrib or modules/composer or something else. 'contrib' is a Drupal-only term, whereas the dependencies in those directories does come via composer, so there's a decent argument for it. There may be other candidates for renaming, or 'contrib' might remain the right answer for this project.

Why should this be an enhancement to this project rather than the userspace?

This is a place where the project could prescribe better ideas than userspace may be familiar with.