Besides, if you make exception-safe code difficult to
write, nobody in practice will write it, so you'll end up
with a system that's tantamount to one that just aborts.
Saying that "Rust the language handled OOM just fine
without stdlib!" and "we can convert OOM to panic!" is
useless when these measures don't help real world code.

I'm not sure where you get the "difficult to write" part from. It's no more or less difficult to write than in any other language, as far as I know; you just do have to go through the effort to indicate that "yes, I did think this through and believe this is exception safe" for types that you want to be able to use across an exception-catching boundary.

As I said, work is ongoing to determine if this AssertUnwindSafe approach is actually workable in practice. The initial implementation had some usability issues, but it looks like it may be more workable now that you can use it on the entire closure if you need to. It's still a speedbump, but a very minor one.

That kind of claim sounds reasonable, sober, and
measured, but it leads to bad outcomes in every system
I've seen, because the "exceptional" case in practice
becomes a hard abort.

Can you point out what these bad outcomes or bad systems have been? I agree that in practice, the most common case is that the exceptional case becomes a hard abort, but I don't necessarily agree that that's a bad thing.

For people who are not trying to write extremely fault-tolerant code like SQLite, and going to great lengths to do so, that is a good thing; adding some half-assed normal error handling around these truly exceptional cases is more likely to lead to mistakes and problems down the line than just aborting is.

For people who are trying to write extremely robust, fault tolerant code, you can either handle panics, or avoid the standard library and do error handling via results. Both should approaches should be viable, depending on your requirements; the standard library does take exception safety into account, so it shouldn't on its own cause issues if you handle errors via panics.

I'm not comfortable to casual changes in core runtime
semantics.

But you are comfortable with the sheer amount of undefined and unspecified behavior in C and C++? Remember, at the moment Rust only has a single implementation and no formal specification, while C and C++ have many different implementations, and the standards allow very wide amounts of leeway in how implementations differ.

Now, Rust not having a formal specification or multiple implementations is not a good thing; it's just a fact of life for a language that is not yet very mature. But I think that this particular behavior is something that should be considered similar to unspecified behavior at the moment. Just like out of memory situations or stack overflow behave differently on different platforms in C and C++ at the moment, how the Rust runtime behaves on out of memory could also be subject to change or different implementations. Given the standard library API, you couldn't return a result, but either aborting or panicking would both be consistent with the language as currently defined.

People (especially from the GNU/Linux world) constantly
assert that allocation failure is rare

I'm not asserting that allocation failure is rare. Just that there are some cases where you don't have a chance to handle it at all, like GNU/Linux where you overcommit, and that handling it in any way other than abort is rare.

SQLite [1] and NTFS [2] come to mind, as well as lots of
tools I've discovered.

Neither SQLite nor NTFS use exceptions, nor are they applications, so they aren't very good examples of applications using exception handling to deal with memory allocation failure.

SQLite is written in C, which doesn't have exceptions, nor a standard library similar to the C++ or Rust standard library. SQLite has had to implement all of their data structures by hand. You can do exactly the same in Rust by using #![no_std] and just using the core library, which only defines basic data types and never allocates.

NTFS is written in the NT kernel, which doesn't have support for exceptions either, nor does it use the C++ standard library.

So yes, you can actually write code that handles allocation failure properly. The examples you've given both eschew a high-level standard library, and instead implement all of their data structures and memory handling themselves, reporting errors by passing error values back. All of which you can do in Rust using #![no_std].

Meanwhile, there are lots of user-space applications that people use all the time which have no special handling for OOM situations; they rely on the OS to provide them with sufficient amounts of virtual memory, and either be killed by not handling an exception, aborting explicitly on getting NULL from malloc, or being killed by an OOM killer if they exceed the capacity of the machine and try to access an overcommitted page.

I'm sure there are some examples out there, somewhere, of user-space applications that actually do catch such issues, and attempt to do graceful cleanup. On the other hand, I don't know how successful they will be, especially if they have to be cross-platform; since any kind of cleanup you may do, such as writing state out to disk before dying, will hit the kernel's page cache, which may involve allocating memory, which may fail in such a situation, even if you do try to handle the issue gracefully in user-space you may not have anything you can do.