Since this introduces a deprecation and will ultimately produce a breaking change, it's ineligible for a fast track proposal. It'll need a full proposal document, and we'll have to have at least some amount of a public response period before we start landing implementation PRs.

@nex3 this is not a fast-track proposal. The proposal has been submitted in #3749, which has been marked as accepted in April, but without updating the spec (this PR fixes that mistake done when marking the proposal as affected)