It's not a hypothetical, it's here in Node 23: https://nodejs.org/docs/latest/api/typescript.html#typescrip....
Speaking about the specification, it's a proposal. Yes, some run ahead and implement proposals under experimental flags, doesn't make it any more/less hypothetical as the proposal can still be rejected rather than progressing.
Come on, now.
> maybe in the future JS runtimes might be able to strip away types for you without a build-step.
You can't backpedal from that to "speaking about the specification". It's not future JS runtimes. It's a thing you can take advantage of right now.