Fog expounded upon my comment perfectly. There have been some games that have tried the sandbox PvP design, but they came and went for the exact reasons that Fog stated. You can blame lack of funding, poor management, poor design, poor execution... player entitlement, and often its some or a little of all of those, but getting a new MMO game out on the market and viably profitable is like playing the Mystic Forge. The promise of that Legendary item (game) is so tempting, but its a costly process and you'll may just not ever get it.
Apply that to a real life scenario, where you have investors, bills, salaries and tons of monetary and time expenses, and ... well, sadly the odds are against a MMO's success before its ever off of the idea table. As gamers and players, most of us really don't even think of that, much less understand it. We just see a game idea that we can get excited about, and expect it to magically happen and fulfill all of our gaming dreams.
Several years ago, I had some venture capitalists approach me. They wanted to get in on the MMO scene, they knew of my expertise through my father and wanted to know the viability of funding a project and whether or not I would design and lead it.
I turned them down and educated them on the volatility of that sector of the gaming market and the risks. The market was highly saturated, there were several projects that were closing, some games that had launched and shut down a few months later and I felt that it was not worth the risk.
So yea, its all fun and games for us, but real money and real risks for the folks behind the scenes. I try to not be too critical, but sometimes I see the same mistakes being made, over and over and over and... so I get a little exasperated and vent. :)
So all of that said, the closest thing you will find to what you want, are the MOBAs. Planetside, SMITE, LoL, DOTA2. Even the Firefall folks got spooked by Beta feedback and decided to implement a PVE element to their open world content. They seem to have actually attracted more players, so at this time, it appears to have been a good decision for them.
Darkfall. I was very critical of that project in another thread and I have not changed my mind or opinions, so all I'll say here is that I wish them luck with the redeux.