In reply to Matt Mullenweg.

Matt Mullenweg, I think you should have no person picking them, but an algorithm.
I would calculate a quality index to decide when a theme should be considered as featured.
The algorithm could take into account some parameters like the number of active installations, reviews, activity on the support forum, automatic tests on PHP and JS warnings, automatic basic test performance and so on.

The algorithm should take into account parameters based on the user's satisfaction and objective evaluations.