Unfortunately, it seems like the final Shard resources are something like ShardResourceType while the rest were just ResourceType.
I totally didn't even spot that. That's what I get for not reading properly, I guess. I decided to try to see if it was possible to create a shard clone that is just the same as a normal shard, but is an ordinary ResourceType instead. It crashed Elemental on worldgen. 
More testing required, methinks.
e: Huh. Guess I must have screwed up somewhere and missed a tag when I was converting the shard from ResourceShardType to ResourceType.
Sovereign with free air shard.
Just rename that file to a .xml file (I changed it to .txt to stop the browser from trying to parse it, bloody stupid thing) and stick it in the units directory. Hopefully I've covered everything, I think.