Who the heck knows, but my best guess is: down the road a bit, when Russell is playing well, Cubs move him to extract some value and, essentially, replace him with Hoerner, who they love (assuming Hoerner continues to develop).
Clearly, Javy can handle SS, Hoerner move to 2nd...maybe in a rotation.
They will feel good about helping Russell rehab, extract some value for him, and replace him with a guy in Hoerner who can, possibly, give the clubhouse a nice boost of energy, at the very least.