We had some conversation at Oslo Hackathon with @noisy about this. His suggestion was to pay for private messages in order to get your message higher priority. This would also solve spam attack! Whale would receive 100+ messages per day from users who wishes to get upvote or attention, and if you want to get your message higher priority or friend of that user, you would do so by sending higher amount and he would see your message as higher priority and can choose to reply you by sending back same amount or none... :))