A thought of a system that could engage players in long term pvp play. It should be reasonably rewarding while being somewhat mysterious.
What came to my head was the TTT2 lucky box system where on successfully finishing a battle you get a chance to receive a lucky box (up to 8).
there are 5 box types:
3 are filled with a small amount of gold
1 with a content unlock
1 with a star (extra gold)
The content unlock could be replaced with a gem anything between a flawless square up to a star. even banners or extra pvp content could be an option here. 8 boxes might be to many for diablo 3 though i can see how trying to get a full 8/8 could be a great motivation to play.
I can see people talking about how good their lucky box streak was the last day. together with a good matchmaking system that could make for a very interesting game topic.
PVP does not need a match making system or rewards.
1st. It needs a lobby system where you can check others gear. This lobby system should be simple where 1 person makes the game, becomes leader and can choose to kick anyone they want prior to game start. Also, the lobby leader can make the game private or public.
2.) Keeping track of wins only, NOT LOSSES. Winning is the only stat that should be recorded which would be useful in finding good players to duel. If stomping newbies is that players thing, then simply play against players with no wins. If a player is looking for a challenge then high wins is a clear sign of a good fight.
The only reward for pvp should be the actual battle. Rewards promote stupid players doing stupid things. Such as boosting. PVP should be kept true to its core. Which is PVP. Thats your reward, the love of the fight.