"I understand that carbon fibre necks..."
"I know for sure that Crimson guitars use both"
roger that... feel free to comment on things I DON"T say! Perhaps you are having your own conversation over there!
yeah, no, carbon fiber rods might be a good idea too. also carbon fibre is not like bret favre.
"Rods are apparently round. "
https://www.stewmac.com/Materials_and_Supplies/Truss_Rods/Carbon_fiber/Carbon_Fiber_Neck_Rods.html?utm_source=google&utm_medium=shopping&utm_campaign=2020-04-gp&gclid=EAIaIQobChMIy62k6JDH6AIVF8RkCh37wAP7EAQYASABEgKq7fD_BwE
stew mac, bitterroot, and the entire guitar community does not agree with you, but for the record I do... rods are round.