Villagers should give out quests, like a blacksmith will have you mine a certain amount of ores and will give you a good enchanted weapon or armor, or priest quests will give you a certain of potion, etc. Quests will give you a good amount of exp. enough to level up once or twice. The items quests give you should be what normally be challenging to get or something you can't get yourself. If there is no more quests, they will be new ones every 2 or 3 Minecraft days. Adventurers are villagers that go out in the world and if you don't live near a village, you can find an adventurer who can lead you back to his village, and he will have a special quest for you, like to a certain new boss that could be implemented into the game, the Giant Golem, this boss can be found in his deep underground fortress. Haven't thought of the mechanics of the fight or the way he acts. But yeah I think this would be an extremely cool feature to have.