As my username hints I'm something of a Ducati freak and CF is the sportbike version of chrome... so I'm not a big fan of it in general. It's overused and often not a great material to choose for the intended function of the part. Along those lines I wouldn't use a composite neck plate. I'm no expert but it seems to me if I wanted to crack a thin carbon fiber sheet, putting countersunk holes in it and screwing it down hard would be a great way to do that.