Carbon fiber moves.Anyone who ever put CF rods in to aid stiffness can tell you that you can still adjust the neck via truss rod...very easily in fact.The only thing CF has that wood does not is an added "memory" so that it tends to try to stay straight.Some woods are stiffer than CF.
Only the truss rod gives you the ability to actually move the neck to counter movement that may come up due to humidity,temperature,or even just an eventual refretting.
"Tradition" is just a keyword being used in this topic to explain away the fear of routing a simple channel.When you say "tradition" you mean "old" and the inference is that you have fresh,new ideas...
No such thing.I have been on this site 10 years and have heard the same exact assertion from almost every guy who starts without woodworking experience..including myself.Without a truss rod your guitar will be less useful than a similar guitar with one.It is a cold,hard truth.Once you get over your fear and lack of skill,you will laugh at yourself for ever thinking it was difficult.
Like Pros said, It was invented to counter a specific problem and it does it well,and the two way rod is so simple to install and use that you would be foolish not to.Hack at wood and cry about tradition all you want,but without a truss rod all you will have built is a guitar shaped piece of art for the wall that anyone who buys will only curse you for selling them once the need arises for adjustment.
If you want to be "fresh and new",invent a thinner,stronger two way rod that still installs in a straight channel