Yeah, that would be nice too!
The idea is NOT to ship these themes with any flavor of the Core, but have avaiable custom core themes for those who want to use it.
In the path of the Core, I suggest it to be lightweight themes, maybe flat ones... not because of the actual "flat tendency" but because flat designs requires less memory and processing (as Core does) and still can be used in slow machines.
Maybe if we have a topic about it in the forum, we could mount an Artwork Team too, users could send mockups...