IMHO only DJI (or other specialty manufacturing with appropriate tools) can come up with a 100% CF shell that is precise enough for flying the P3. I´m experimenting a lot with it at the moment but I tell you, that´s one tough task. I´m no CF expert or anything but I´ve been molding stuff for some time now and this is another level, at least for me.
If you look inside it´s a hell of job, a seriously sophisticated piece (i.e. extremelly complex with all the reinforcement ribs, recesses, angles, screw beds, etc.) A molded CF shell doesn´t have to be that complex b/c it´s stronger and more rigid. But still, the small tolerances, not to mention the motor bases, make up for a complex part to mold without advanced tooling. At the very least it´ll be time and labor intensive, implying high costs.
For example, if the motor base angle is off by a few minutes it could interfere with the flying to the point of making the AC uncontrollable. Or if the openings are wrong it could cause heat buildup or something. And to make it realy, really strong and rigid and balanced, it would be ideal to use pressing techniques on molding. Even with the potential scale that would cost a lot for anyone but DJI maybe.
IMHO untill DJI comes up with a CF shell (if ever), I believe it´s much simpler, faster and easier to add reinforcements to the inner part of the original shell. Specifically around the lower motor base and arms. In theory only a bit of epoxy on the area would work, but of course a bit of glass or carbon fiber or any other lighweight fabric strategicaly placed would add structural integrity and rigidity to the shell - without adding weight or bulk. That may be needed on really bad shells as some we´ve seen around cracking like eggs.