I'm happy to announce that Quick Navigation now comes as a default feature in DocC-Render and is available in both 5.8 dev and the nightly toolchain 
After requesting the enablement, Quick Navigation made it into the main and 5.8 release branches last week, and, as requested by the project maintainers, could still be disabled by the developer through the theme-settings.json file.
Once again, thank you all for helping me build this!