We should modify the menu structure so it stores an "admin" flag for admin pages. This should be editable from the menu screen, 'cos for eg. it depends on site whether node/nid/edit is admin or not. To save a lot of typing, we could define that all children of an admin page is also an admin page.
When this is in place, we could do the admin theming as discussed in Antwerp: if the page is an admin page, the theme system would like into the directory of the current theme for an admin subdirectory and fetch the admin theme from there. It would be not be a necessity, we would provide some defau