[moe]

Can we contrive esoteric situations where this feature would fail spectacularly? Yes.

Do they matter in reality? No.

Make it an optional feature to be toggled with an interpreter flag. People like me can turn it on, you can keep it turned off.

[army]

That doesn't seem that esoteric to me: in general the problem is that repr() can result in execution of arbitrary code, and that there's no way to cleanly and reliably terminate arbitrary code. This includes Python code: it's possible to terminate it at an arbitrary point, but that leaves things in an indeterminate state.

I think it's pretty important that you shouldn't add features with unpredictable behaviour into the core of the language, particularly into error handling code.

[moe]

It's esoteric because in reality it's the kind of bug that never happens. And if it happens it's trivial to identify the cause; "Oh, it hangs in the middle of a strack-trace, what could it possibly be...".

Why would your code contain repr()-functions that trigger "unpredictable behavior" to begin with anyway?