Bounty hunter mod eh? is this anything to do with the hunter mod?
ok- this is an ambitous idea but...
set solely in village/town maps- populate the map with villagers who are neutral to the action, but flee from combat- guards who will attack anyone if they are seen to fight (will be a ***** to code).
played with a small number of players and no definate sides- the teams will be 3:1 ratio in favor of the bounty hunters
The wanted team can work together if they wish to survive, but often it is best to split up to evade detection. they are much weaker than bounty hunters, armed with crappy weapons and weak armour- allthough if they take an unaware hunter by surprise they can land a kill (and steal their weapons

)
the bounty hunters- whilst on a team they are actualy competing for the kills, they can kill each other to remove competition (but dont score points from that), their only goal is to kill the wanted players- earning large amounts of gold for each kill.
well equiped with a wide veriety of equipment.
^ its an ambitous idea, but it would rock XD
EDIT: how about something a little similar to The Ship (if I recall correctly) and a little more do-able
its a deathmatch mode basicaly, large numbers of players in town-like levels.
each player is given a target to kill - only they know who that target is. but allso every player has someone after them
you gain a point if you kill your target (that target then changes), you lose a point if you kill someone who isnt your target- but, you dont lose points for killing the person who is after you.
what you get is a paranoid game, going after your target without letting them know you are after them, but allso constantly checking your back looking for your nemesis.
equipment will have to be carefully selected and maps will need to be well laid out. I suggest everyone wears civilian clothes and are armed with knives (that instakill) and hand crossbows (that are hard to see, so its hard to see if someone is aiming at you)