For what it's worth, Perl (5) has the same problem as CPython. Accordingly, there's not only heaps of allocation- and ref-counting-avoidance optimizations (eg. the stack isn't recounted) but also heaps of bugs from the optimizations. Again, the (main) stack not owning references is the biggest source of these bugs.

The problem with predictable destruction, we typically called "timely destruction", but more accurate would've been "immediate destruction" and if your language guarantees it, it tends to be great for automatically releasing resources (memory, file handles,...) in a lexically predictable manner. Softening any such guarantee should lead to entertaining resource races magically appearing in the real world. It occurs to me now that I never checked what pypy guarantees if anything?

We (Perl) never really came up with a great strategy for working around this (you tended to get the worst of both worlds in most naive reimplementations of the behavior in a GC-based interpreter) and while I certainly haven't tried to work out a clean argument to the effect, I'm fairly convinced it won't fly at all.