Bingo.
A lot of others in this thread couldn't envision a use for this, so they automatically think it is a stupid idea. I didn't jump to your use case, but I am open minded enough to believe that there might be a use I wasn't considering.
I'll second that 'bingo'. This is likely nothing more than a fringe use case... but that doesn't mean it's not an important use case.
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What exactly should Apple do about a yet undeveloped 3rd party SDK that may or may not be used by anyone?
What 'can' they do? Lots. Apple controls the user experience, so prohibiting this behavior would be easy.
What 'should' they do? Nothing. Every App Developer has the right to block screenshots. Every user has the right to tell the App Developer to pound sand. End of day things will find balance.