*Before starting, I apologize for my bad English. English is not my native language*
Since this latest version focuses on the villagers to make them more viable. I think adding emerald nuggets will improve exchanges. It could work like the typical nugget (Emerald = 9 nuggets). Emerald nuggets could also be found in dungeons, to make the item less rare.
About exchanges ... I think I could use something like:
2 emerald nugget = 1 coal
6 emerald nugget = 1 Lapis
8 emerald nugget = 1 redstone
1 emerald + 6 nugget = 1 Iron
1 emerald + 8 nugget = 1 gold
What do you think?