With the update to Habari 0.9 (developer edition) comes a temporary (read: "in transition") design as well, which is a modified version of Charcoal. It'll become the base for "Agent Magenta", the future theme of AlltagsGrauen 8.0.
About themes in user directory: There seems to be a not so easily detectable bug - when I tried to simply copy the original Charcoal theme residing in the system directory plus additionally changing just its name and class name (including a full theme-directory wide search-and-replace), Habari did act up afterwards, displaying the following error over and over again:
InvalidArgumentException: Passed variable is not an array or object, using empty array instead in /system/classes/format.php line 270
This seems to be somehow related with Bug #233, which is to be found in the Habari Github bug tracker. I "fixed" this issue by copying the theme once again, NOT changing the class name but just the theme name plus prefixing the original Charcoal directory in the system path with a dot.
Another negative thing to notice is that the custom permalinks (RN Custom Permalinks) seems to have stopped working - I prefer post IDs over full outwritten post slugs :(
Update: Applied a temporary fix for this using the route301 plugin. Not really satisfying, but at least redirects from the old site (AG 7.0) should work again :)