Internal Cross Channel links in Channel Manager "Edit Menu" UI

In the "Edit Menu" UI (as seen in the Channel Manager when changing navigation items) only sitemap items of the current channel can be selected. To provide CMS editors with the ability to use Cross Channel links there should be a configurable option of selectable Channels in the dropdown.
As a first step it would be sufficient if we could provide editors with the option to select sitemap items of any channel.
External links are no option as they (semantically correct) open links in new tabs.