This is a really interesting comment, could you elaborate on it a bit more? Which part of a deterministic universe would the halting problem serve to enable free will? -The universe as a whole? -Any agent claiming to have free will? -Some physical process that couldn't be simulated faster by something else in the universe?
Free will is just what it feels like to have a mind that can construct models of realities that are not fact. And you can model nondeterminism in a deterministic system just fine.
So I would argue that it illustrates nothing of significance under either of those issues.