The idea for this proposal comes from two basic concepts.
One, I like dinosaur mods and animal mods, and it'd be cool if having dinosaurs in your park generated income, and two, the thought of setting myself up as god-emperor of some village somewhere and taxing all the peasants in payment for being the only one around that actually does any work is very appealing to me.
What I'm thinking here is a special kind of nametag. It makes the mob tagged with it drop emeralds at certain intervals, depending on the mob's current health. So, for example, your 250HP T-Rex will bring in more emeralds than a cow. In the config settings, the player will be able to set drop rate, amount per drop, that sort of thing.
Now for the more complicated ideas.
Assuming what I described above is possible, I'd also like to add more complicated tags. One would provide a mob with health regen, made by crafting a diamond with an emerald-drop tag to make a better tag, or something. Another, by combining with a feather, will give the mob fall damage resistance. Besides that, mixing in any item will make the mob also drop that item. This is for creatures that require feeding, so for example your T Rex will now automatically generate chicken meat for it to snack on. There will also be the option to combine any of these tags, so for example (if you have the diamonds, and really want your T Rex to stay alive) you could make a tag that provides the emeralds, feather falling, regen AND chicken meat (or whatever meat) dropping.
The second bit there is obviously a long way off, and might not even work, but it's an idea after all.
Problem is, I don't know anything about modding. Help/links to relevant tutorials/input/telling me there's already a mod that does this will be most appreciated.