There has. It was called Vanguard Saga of Heroes. No, the majority of mmo's released fail in the mind's of "most players." Failure is subjective considering most people view failure as "Not beating WoW." You realize, those same people, also view FF11 as a failure, correct? I've even seen them stated as such on the forums, which is ridiculous. They say "Only 500,000 subscribers? Lol." People have a warped idea of what constitutes as a success or failure. Why do I think it doesn't work? The fact that all these developers who developed their game in that regard have moved past it. Even FF11 did away with it. You might say "They lost faith." but that isn't it. Remember, they have data we don't. I doubt they implemented it and twiddled their thumbs as their player base dropped. No, it's more likely that they implemented modern mmo ideals and did away with the older ones and saw a rise in population. Which confirmed to them that it was the correct course of action. Making mmo's more accessible to the common population is what made the mmo industry so booming as it is.
If an mmo is made, even high quality, with a heavy grind it's considered a "korean grinder." and people push it away like the plague. I played Everquest and Final Fantasy 11. After experiencing the "modern mmo" I wouldn't play a game with that kind of time investment ever again (despite playing EQ for years.) I'm not alone.
Note when SWTOR one of the biggest complaints was "No dungeon finder?" Again, think about why FF11 changed it's model. Think about why they didn't use the original FF11 mold for this mmo. Think about why no mmo uses that model anymore really and why even sand box mmos which are a totally different animal are trying to find ways to hide/remove grind?
Here's the thing it worked in the past because... those kind of mmo's with massive leveling grind were the only options. It's not anymore. Most people opt out. Most people want to experience end game.