One of the ideas of bounty award was that bounty was awarded in conjunction with completing story arcs.  Not all arcs would be GM driven - but at the beginning of a storyline, whether between players or GMs, you could send a short post to the gm, a 'size' of the arc could be determined, (minor, moderate, major, jaw-dropping epicness) and a variable bouny reward.  After the arc is complete, there'd be a reward for it; this ties bounty to a character's actual progression, not a mechanical amount of time, and directly rewards activity in the game.