The HIP asks to make the Policy Markdown and store it “somewhere”
What do you mean? The HIP states that the Markdown is kept and modified through a repository. The HIP does not dictate any official repository for this, but recommends using the Proof of Humanity github project to host the repository.
Then, the initial Markdown file will be posted as the Policy in the MetaEvidence.
I’d recomend to wait until HIP-51 is passed and finished, and publish this Phase-3 using the Poh Library to store the Markdown on IPFS on that Library.
The precedent for “Policy storage” is that they are not stored anywhere. This was not a concern in this HIP. Technically, you can access just by checking the last MetaEvidence in the PoH contract. But, if in that HIP a process to formalize official PoH storage will be done, then, this HIP-51 should make the specification for the Policy as well.