Carbon fiber is great. Worked as a CF tech for many years. I even braided it from unitape to make panels. While it is great it is not magic and it has limitations. Like generally speaking, if you cut it- like for a hole that allows a bolt to pass through- you weaken it.
A roll cage out of CF? That would need to be some large co-cured structures, unless the CF goes into a trunion or similar and is bonded, not bolted.
I don't see it being practical for a roll cage, and as far as weight savings goes, my experience tells me that this is similar to the Corvette myth- that since fiberglass is light and the Vette body is made of fiberglass, the Corvette is a light car. With CF, don't forget that there would be almost certainly supporting structure that weighs something and how do you inspect it? Every joint is suspect, everything that touches it might cause wear due to vibration.
Driving and working on a Sly 2008 Solstice GXP 5spd 260/260, and the worst-built 2012 LS3 Camaro 1SS to escape from Oshawa.
Gone but not forgotten:
2007 Solstice GXP 5 speed 290/340
Stored and needing to part ways with a 1970 Skylark Custom convertible I have owned since 1989 and turned into a GS455 clone. 462 with 7/8 primary headers, adjustable roller rockers, TA Performance Stage 1 aluminum heads, auto, Chevy 12 bolt, 3.31:1. Sadly a project car now but a driver from '89 to '06.