I've always liked the ideas of having swamps in Minecraft but they don't really serve a purpose (like most biomes in Minecraft). I think there should be Swamp villages that would function very differently than regular villages. Swamp villages would have access to special swamp boats/ships that they would fish out of, you could buy the fish from the village for wheat (because they can't grow it in swamps). I
If you can build the villages and send me the schematics or the world itself, I think I can help. I don't know about the specialized trade though, as I'm not a very experienced modder. More of a skilled ameture.
Mod ideas to improve swamps...