Questions
1. Is anyone already working on RFC 9666 in the community that I should coordinate with?
I'm not aware of anyone else working on this; let's see whether there are replies to your email.
2. Given the Experimental status of the RFC, how would maintainers prefer this to land — a feature-gated series of small PRs, or one larger PR?
In general, it's easier for us to absorb smaller, "incremental" PRs, just for practical time-to-review reasons. If it's possible to offer work in increments, that'd be helpful.
3. Would you prefer I open a GitHub issue to track the design first, or go straight to a Draft PR for directional feedback?
It's not required to have a "tracking" issue, but it can be helpful, to supply a common rendezvous point for doc references, discussions that might span multiple PRs, etc.
Thanks,
Mark