What is apple’s *official* recommendation on MacBook Pro shells?

You're not communicating with Apple when you post in the Community. Apple support or customer services representatives do not participate in these forums. We're all just fellow users, helping out as we have time and knowledge to share.

As for what I, one of your fellows user, would say, it's that it depends on the specific case and how you use your Mac. If you regularly push it to its limits, then yes, a case could make the Mac more prone to overheating since any case, even the thinnest, is going to be somewhat insulating, though a properly designed case will at least not block the cooling vents.

The same would apply to the screen hinge; a properly designed case from a reputably vendor should not put the hinge at significant risk.

But there are dozens of not hundreds of cases on the market and not all of them are from companies that have put in the effort to make sure that their cases fit and work properly. Go with a company such as OtterBox that is very experienced and highly regarded in the market and you should be fine. Should you encounter heating issues during heavy load, you can always remove the case temporarily.

Regards.

First, you're not talking to Apple here. While these forums and owned, run, moderated and maintained by Apple, everyone you speak to here is another end user.

Yes, I see all kinds of third party shells. You'll have to look them up by brand and model to see what other folks who have purchased and used them think of each one.