I have an idea that i'm not entirely sure will work but i'm hoping to discuss openly to see if its feasible.
I aim to have a subdomain that is for groups in our area so will use the organic groups module to achieve that task.
One thing i think would be unique is the ability of group admins (the ones who created and / or maintain their group websites) to have access to other themes and blocks they can display to make their sub websites unique to them.
Themes are easy as its part of the module to allow a group admin to select available themes and (hopefully) if i can find a way to grab the missions and group titles from a group to provide a global variable, i can adjust templates so each is unique, or as unique as it should be.
Then i can just print a $og_mission where a template header would be and, coupled with IMCE and TinyMCE, would allow them to upload images and design their own unique header to any given template.
see http://drupal.org/node/104199
Now blocks are slightly different but i do have some ideas here.
As you know blocks can be set to allow members to turn on or off their visibility in their members profile. I'm wondering if this is where we could use a checksum to allow rendering of premade blocks on a per group admin basis, set through that admins profile.
How it would work is that as global admin i would present a number of blocks that groups could use. These blocks will be switched off or on in a default state of my choosing. Now the group admin may not like some of the blocks or may prefer some that are not activated globally at the offset. So they go into their profile page, tick a box or untick a box and BHAM, the block shows or doesn't show on their groups home page to everyone.