Yah, if you'd like to write up a proposal repo for this, I'm interested. Basically you need to hit "Use this template" on GitHub - tc39/template-for-proposals: A template for ECMAScript proposals, and fill out the readme with details.
Yah, that's what was landed on in the #tc39 IRC channel. But it's not free (some runtime processing and WeakMap lookup), and will conflict with the "templateness" in proposals like GitHub - tc39/proposal-array-is-template-object: TC39 proposal to identify template strings. I'm not super excited with this approach, but it's a stop-gap.