The problem with this question is we're dealing with an orthographic representation of an "imitative/onomatopoeic" interjection. It's worth noting OED's two different pronunciations...
OED list the alternative spellings euuw, euuww, euuwww, euw, euww, euwww, eww, ewww, and point out "forms with u occurring three or more times or w occurring four or more times are also occasionally attested". All this for a "word" that apparently didn't even exist until 1975.
OP is clearly more interested in the history of the sound itself than whether or how it's written, but I do think it's worth noting that OED also says compare ugh, ough, ooh, oh. I have to say that none of those forms seem to suggest the sound I personally usually make to indicate disgust (it's pretty much just an "extended neutral vowel", which I'd normally transcribe as eugh).
I first noticed the "American high school girl" pronunciation (which is how I still feel about it) back in the late 90s, around the time I started using Internet chat forums. But it's quite likely that in all the fifteen years since then I personally have never made that sound myself (except facetiously, poking fun at people who do make it). On the other hand, I bet I've written it thousands of times in forum posts and "txt" messages - simply because it's quick, easily recognised, and "close enough".
Both my children (in their early 20s) definitely use the /ˈiː(j)uː/ pronunciation from time to time, and one of them has just told me she thinks of it as "normal English" (not particularly "American"). But they grew up watching The Simpsons, so what do they know? They both sometimes answer the phone with "Y'ello?", which so far as I'm concerned is a Homer Simpson affectation.
My point here is that it's very difficult to know exactly how other people pronounce words just by looking at what they write. They might be like me, just using the easiest or most common spelling because "accuracy" is unimportant or impossible to achieve. Or they may start off using the "affected" form facetiously to poke fun, but eventually get so used to it they use it "for real".
Or people may consciously attempt to imitate the sound they think is suggested by a particular orthography. On that specific point, when I started writing this section I had it in mind to point out that no-one ever pronounces hiccough the way you'd expect from how it's written. In support of which I was going to post this audio link.
I swear to God I had to turn the volume up and listen real close to convince myself that "Emma" there really is saying hickuff, because my "language processing" mental circuitry automatically switches it to hickup before anything reaches my conscious awareness. In matters of language, we tend to hear what we expect to hear (whether the source is actual sounds, or letters).