Game developers, as well as the armchair developers on blogs and forums, tend to design games around what *they* would like to play. So if I'd ask you for what features your dream MMORPG would have, I'm sure you could provide me a list. But now imagine for a moment that you were an investor, with $50+ million to invest in a MMORPG project. As you can't afford that game to flop, you're more likely to look for features that you think will be popular, and you'll look at past successes. So what do we get when we combine the features of the most popular online games out there? World of Farmcraft, of course, the combination of WoW and Farmville.
In World of Farmcraft (WoF), every player starts out with a farm in a beautiful, large 3D world. He can plant things on that farm, breed various animals, and engage in other crafts. Tending to a farm only takes about half an hour per day, so the ultra-casual players might want to stick to doing only that. But players with more time on their hand can turn their plowshare into a sword, and go on adventuring. Players could also choose to do both, but the skill / talent system would make it better to specialize in either farming/crafting or adventuring, and only do little of the other activity.
World of Farmcraft would be a very social game, with lots of player interaction. Thus quests aren't provided by NPC, but by players. Farms can have problems with various pests, from wolves attacking sheep to threats of orc invasions. Thus farmers would offer a part of their profits as quest rewards to adventurer players to take care of these threats. In the other direction adventurers would buy equipment crafted by farmers. Players would organize themselves not in guilds, but in villages, in which farmers and adventurers need to work together against common outside threats.
What other features would you add to World of Farmcraft, taking basic design principles from either WoW or Farmville and turning them into something designed for maximum popularity for the largest possible playerbase?