I think this is incredibly probable.
Also, has anyone thought that the reason Joel is not a Rithmatist is that he has already developed is individual strengths and therefore he needs to bond with a specific Shadowblaze. One who's strength matches his own. this would also make sense as to why it's easier when they're younger to on because the humans have not developed a specialized skill, and so are open to bonding with whichever one picks them.