So you're asking how much memory this resoource exhaustion attack consumes when you run it.

Each line in the WP examaple amplifies by a factor of 10. It has 9 lines. It's 10e9. That's a billion times 3, which is just enough to 32-bit virtual memory space in common operating systems.

Of course the XML implementation could be smart and short-circuit this while preserving the semantics.