I'd want this backed by CloudFlare's dns, not R53 so that I could take advantage of CF's network as a proxy in front of my servers. https://www.cloudflare.com/docs/client-api.html
https://github.com/dnerdy/namesync
This flat file format seems to work well, and the tool could potentially be updated to support other DNS providers.
It's not impossible we could allow a per-zone destination to be setup, and upload to Google, Amazon, CloudFlare, or somebody else.