>he "how likely is it, really?" response to questions of technical correctness has always bothered me.
But the question is important in another context: language design. Why is this undefined behavior something that exists in the first place? Objects larger than PTRDIFF_MAX could just not be allowed! This avoids the problem and makes code easier to reason about, with pretty much no downside.
I like the way you're thinking, but that sort of thing probably doesn't get past a committee. "Hey we might not be able to think of an application but that doesn't mean our users won't have a legitimate reason for doing it ... Motion passed."
But the question is important in another context: language design. Why is this undefined behavior something that exists in the first place? Objects larger than PTRDIFF_MAX could just not be allowed! This avoids the problem and makes code easier to reason about, with pretty much no downside.