I was thinking, now that we have assassins, why not have an assassination gamemode (maybe even make it optional to include only the assassin heroes in this gamemode)?
Well, in all its simplicity:
2 teams battling it out like normal, only there's no gold awarded for kills. Minion gold/exp awards could be optional.
At the beginning each team gets assigned one enemy player as assassination-target. Only killing this enemy will yield gold.
When this enemy has been killed, a new random enemy will be the new assassination-target.
Of course the players do not know who in their team have been targetted to be assassinated by the other team, so you can "fake out" people, by going all out on your target's teammate, making them think he's the target, urging him to flee to safety. And then pummel the real target when the opposing team thinks they've figured out who of them is targetted.
Conditions for winning should just be a specific amount of assassinations. Like 20 or so. Maybe a scalable number considering how many are in the game.
Any further ideas?