FYI,

I owned my P3P for 1.5 months before I noticed very slight shell cracks in the typical screw holes. I contacted DJI by phone and created a ticket. Yes I was on hold for quite a while to get through. DJI sent me a shipping label for free and I shipped it. Received 2-3 days later and I received an email stating it was received and warranty repairs approved.

7-8 days later, another email saying it's done and being shipped back. Received 2-3 days after. I give DJI 2 thumbs up for turn around time.

Upon opening the box I found the repair on my P3P consisted of simply replacing the lower half of the shell. All else remained the same. A little surprised, I thought perhaps motors might be replaced with new design but not a big deal. I then took a light to the motor mounts to look for the new X-bracing design and found none. Looks like the same shell again to me.

What are the different versions of shell? Should I not have received the newer design X-brace shell? What is going to prevent shell cracks from occurring again?

You won't receive new parts until the old ones are gone.  On the other hand, I'm not sure I would want the new shell.  One post I read said the new one feels much thinner and flexible than the old.  The arms twist, etc.  I think I would be tempted to just beef up the old shell.  I had a slight accident recently, repaired the gimbal mount and wiring myself and inspected it closely while I had it apart.  I had slight spider web cracks around the motor mount screws outside, but they didn't go further than that, more than likely because I had the snap on guards on it.  i put it back together, remounted the snap guard mounts for structural support and keep flying.