Hmm... It would be nice to replace axons in human with these structures. The speed of propagation of spikes will be much higher. I'm not sure that it worth it to replace axons in brains, but those long axons in a spinal cord and in optic nerve can really benefit from the faster signal propagation and reduce the reaction time.

Axons are not just wires, they also do computation and signal processing: https://www.nature.com/articles/nrn1397 Your idea would sinoly not work.