Not much of an insight perhaps, just an observation. Risks are notoriously hard to quantify.

But where there's an attack surface there is a risk. There's logging and parsing of logs going on here.

Does that translate to practical risk, in the sense that your system will get owned in this way? Personally I wouldn't consider it very likely. A Linux box won't get popped via a plain open openssh but likely not via this python log parser either. It's still not a bet I would take.

There's so much going on in a network stack that I would look for bugs there before the same in pre-auth openssh but one does not know for certain until after the fact.