My humble opinions.
Ladder hits should not be bountyable, you're inviting PvP by opting in and responding to it by using a system that is supposed to be there as a method of dealing with unwanted PvP attention
Bounties should not expire, at least not unless they have been up for a silly amount of time like 10 days+ the main thing that put me off bounty hunting was getting abuse from people after clearing them with 10 stams because they were counting on their bounty being left to expire. It seems a fairly pointless system if posted players can get on and off the board with no loss, especially when that seems to have become the most commonly expected outcome.
Counter bounties do often serve a purpose, particularly as a bounty is the best oppertunity to take levels from someone, and if a whole guild or group of people jump on a bounty they may need to be smacked back. I can however see the appeal of implementing some method of standard bounty hunting as a kind of low risk enterprise - since most other aspects have optional low risk versions now. So perhaps a good compromise would be that a bounty hunter could not be counter bountied unless they hit with more than 10 stam. So someone clearing with 10 x 10 would not be counterable, but any hit above 10 stam would make a counter bounty possible.