I also don't believe it can be one-shotted (there's too many deltas between Notion's API and Obsidian).
With that said, LLMs are great for enumerating edge-cases, and this feels like the perfect task for Codex/Claude Code.
I'd implore the obsidian team/maintainers to take a stab at building this with LLMs. Based on personal experience, the cost is likely within the same magnitude ($100-$1k in API cost + dev time), but the additional context (tests, docs, etc.) will be invaluable to future changes to either API surface.