Data driven blocks, structures, and mob spawning

On java, after messing around with entities doing custom spawns with datapacks and I started looking at villages how a player can "make" a village with villagers, beds, and a bell/bed. Allowing iron golems and cats to spawn. It would be fantastic if we can data drive blocks and entities to make a custom structure. We can potentially have these player built structures have different effects or uses. An example I was wanting to do is build a structure in game and this structure can naturally spawn copper golems, maybe even copper golems with custom attributes.

Another thing I was wanting to do is data driven blocks or game events like custom stone generator or even events like a couldron being filled with powered snow instead of water in a rain biome.