As a former bicycle mechanic, and current carbon fiber neck enthusiast, I'd like to clarify something which was brought up:
Typically, carbon fiber necks are not used for their incredible lightweight-to-strength ratio, as they are on bicycle frames, boats, race cars, etc.
They are usually built in a way that keeps them sturdy and reliable, but either tend to be somewhat thick-walled by comparison or molded over some kind of core.
Bike frames are rather thin walled for sure. I was able to cut through a few trashed ones back in the day and was always shocked at how strong the stuff was, while still being laid up thin like that.
But in necks, I'd either feel the heel or headstock thickness when screws needed to be installed and it was laid up thicker.
I've dealt with MANY of the various carbon necks over the years and not one of them was scary light. Most are either similar in weight to wood (Status for sure) or heavier (Moses or Peavey G Bass).
When I would bring my basses into the bike shop back in the day, the bike guys would ask about the weight, which is why the questions above struck a chord with me. I'd hand them the bass and they'd be like "...oh, okay" and hand it back.