Compiles, can get ingame, uses Mixins to work around missing Fork Hooks for structures and custom dimensions.

src/main/java/appeng/mixins/StructureAccessor.java

@@ -0,0 +1,16 @@
+package appeng.mixins;
+
+import net.minecraft.world.gen.GenerationStage;
+import net.minecraft.world.gen.feature.structure.Structure;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.gen.Invoker;
+
+@Mixin(Structure.class)
+public interface StructureAccessor {
+
+    @Invoker("func_236394_a_")
+    static <F extends Structure<?>> F register(String id, F feature, GenerationStage.Decoration defaultStage) {
+        throw new AssertionError();
+    }
+
+}