as you probably know there are plans to unity Classic UI, Modern UI and the control part of Paper UI into a single application. Unfortunately the current sitemap mechanism is textual configurable only and the REST interface (that is used by UIs) is not prepared to support modifications. To be more user-friendly for newcomers the idea is that the future UI can however let the user manipulate the sitemap by a sitemap-builder or by live-reordering of sitemap elements etc.
For compatibility and migration reasons, the old sitemap and the new sitemap interface need to coexist for a time. This thread is about to find a name for sitemaps2, that can be used on the REST interface and in the user interface to distinguish it from “sitemaps1”.
This thread is NOT about to discuss if that makes sense. Please open a second thread if you feel the need to discuss that.