Huh, I don't know about that. The way I envision in it my mind, the Shards are each a fragment of creation. Their Intents are sixteen different aspects of creation. I would doubt that there are Shards which are kind of mixtures. Shards are fundamental, as far as I know.
Hi Fell!
I suppose it is possible. The existence of such a quadrant would largely depend on where Ruin lies. So, here's some food for thought: if Ruin and Preservation are in separate quadrants, what made them such great opposites that those two had to be together? Meaning, why couldn't Ruin balance another Shard in the quadrant Preservation is in?
The way I see it, there is a deeper significance to Ruin and Preservation's pairing, and I think a model which inherently pairs them from the beginning explains that significance much better than "well, they are in separate quadrants but there was something else which drew them together." Might as well reduce a degree of freedom.
(Plus, Preservation does not seem to enhance things. I suppose you could argue that Allomancy enhances an Allomancer, but that's bad logic, because pretty much any magic enhances its users )
The way I read it, Ruin is Entropy, and an Entropy Shard wouldn't be distinct enough to work.