From reading the proposal, previous thread and along-side thread an task locals, I have an impression that deinit async (and I see in previous review also were "votes" for it), or any other explicit mark (isolated(unsafe)? makes not a lot of sense though) that this change will make an effect on how deterministicaly deinit is executed. IMO isolated in that case has less expressivity over async, but latter brings also the need to support other asynchoronous operations, which might be too much.
I also support this take on importance of documenting, as it might be not clear (especially to newcomers to the language) to understand why this feature exists and what aims to address.
Aside from that, +1.