I think the point made by 2 or more people here is that this non-standard feature has been shipped to half of Chrome users. That feels much closer to shipping to them all, than to shipping to say just Canary or Dev or even Beta users.

To some extent this might be a matter of appearance. Does Google have a firm rule against shipping a proprietary protocol to over 50% - is that why you stopped there? If so, that would be reassuring to hear.