We  will prefer  

- themes which has versions for drupal 6 and drupal 7 distributions

- themes must work correct in IE6 ans above, Opera 9 and above, Firefox 2.0, Chrome  and Safari

We interesting in simple good looking drupal themes to give people possibility get normal standalone blog in seconds.

Later I add requirements to theme regions or requirements to description sets of theme regions(e.g. where place navigation, primary links and something else - I plan organize presets for each system theme where it is possible).