I suggest that we get a little store at spawn with 1 of each villager, or like Primordia we can order villagers with a set payment for a town.
I'm not sure if anyone has realised, but replacing x amounts of stone with Emeralds wouldn't actually work as well as you think, doing something like //replace stone Emerald_ore 5000 doesn't determine where the Emerald ore is placed, you would have to randomize the selection or manually place it in, all in all, it isn't a clever idea and is much easier for users to just trade villagers and give them items for emeralds, Unless you replaced a current ore that is already in the game.