Realistic villager currencies

Different kinds of village should have different sorts of currencies. For example, coastal villages would have nautilus shells, and desert/savanna villages (being close to badlands biomes) would trade gold nuggets. Just to add a subtle layer of realism.

Emeralds should be kept as a universal form of currency for two reasons:

1) Village-specific currencies would be slightly more obtainable resources, whereas emeralds have the advantage of being used in any village, no matter what. I think that keeps it nicely balanced.

2) If emeralds could no longer be used as currency, their only application would be in the construction of beacons, and no one uses emeralds for beacons anyway.