Why, that's obvious though, isn't it? Who would pronounce 'cooperate' to rhyme with 'recuperate'?
A very significant number of people pronounce 'zoology' in exactly that way. With the spelling 'zoölogy', it's very clear that the correct pronunciation causes it to rhyme with 'oology'. Of course, even if people realized that the first syllable was just 'zo' it's just as reasonable that they might pronounce it, not knowing better, like 'to' or 'do', rather than 'go', 'no', 'so', or 'yo'; so it might not help much anyway. Still though, I say we bring it back. Everyone join in on the great diaeresis rennaissance!
"Yeah, yeah, Div," you say, "don't get all pedantic on us. You're not perfect."
Of course, I'm not. Only tonight did I also learn about 'aërial', which is embarrassing, since i had been pronouncing it with only three syllables to rhyme with the name 'Ariel'. Oops. Maybe that's an argument for using ligatures for vowel dipthongs, as in 'diæresis', but that's another post.
Real update to follow in a matter of days. I promise.