Privacy: Won't meaningfully impact privacy. HN like any forum is a bad place to post your secrets simply because the servers are not yours. Post history for each account is already visible, so if you have an agenda, it sticks out like a sore thumb there.
Moderation: Won't meaningfully impact moderation. HN can already see this info and they are the ones that take moderator action. It may hurt moderation/increase moderation costs because people may tend more to report content based on country instead of content.
Transparency: Outright influencer content (political or corporate) doesn't make it to the front page enough for it to matter, or if it does, I can't tell.
Anti-abuse: Same as moderation. Abuse reports should be processed based on content and not country of origin.
Meaningfully improves discussion quality: If a story is about something happening in a particular country, people who look like they are from that country might get asked more or different questions. This puts people from that country on the spot. They may get increased unsolicited communication or thread hijacks. Right now, if someone wants to be on that spot, they can voluntarily identify, either in the profile or in the post.
Possibly something useful would be a rule/requirement that claiming to be from a country different than the one you made an account from--seen either in a profile or post--requires verification for further posting, but if you never make such a contrary claim, the verification is not needed.