Sounds familiar to me. I started the Selenium project (original version was written in JS), started a company around it (Sauce Labs). Browser vendors implemented the Selenium WebDriver protocol, and now it's a W3C standard for browser automation. So, yeah.
(Note: Massive generalization of the project history though, including the part where I and other key project members worked at the browser vendors at various times. Having insiders at the browser vendors does massively help move a standard forward.)
I'm more pessimistic. I'm wondering: Has there actually been a case where the "company founded around that hacked-up JS implementation" for a non-trivial feature did not happen to be one of the browser vendors themselves?
I used to lurk on the WHATWG mailing list and while the amounts of improvements they did to the web cannot be overstated, their descision-making process always seemed to be opaque to put it mildly: Features brought up by users where often debated back and forth without any clear goal until the spec editor basically said "we'll add it" or "we won't add it" with no clear reasons given. Other features "hit the ground running" that were apparently decided elsewhere and were only presented in the mailing list to discuss implementation details.