Since he's not actually playing for an NFL team, his value right now is zero.
If he were to sign with "the right team", like Chicago for instance, his value would instantaneously skyrocket.
If you're planning on waiting until he signs then scooping him up, that is a terrible plan.
The only move right now is to drop one of your scrubs and pick up Dillon in hopes that he signs. If he doesn't sign with anyone, drop Dillon and pick up one of the many other scrubs that will surely be available anytime. In this scenario you risk virtually nothing, and could gain a proven veteran RB on a run-first Super Bowl contending team with a great defense.
Zero risk + high reward = Good move.