IMHO Japanese going for long vowels is probably not a good change
I'm not a native Jp speaker but I'm somewhat familiar with it at least.
First, if you write them in katakanas, they all end with the long-vowel stroke! which isn't helpful at all but takes more space.
Second, there're plenty of words with long vowels. Mass long vowels don't resolve homophones with other words more than introduce them. Writing them in katakanas is sufficient for the purpose of disambiguation.
Third, for a feeling of magical calls, alien tongue, or the like (I believe that's the appeal of color notation), I never see mass-long-voweled verses practised in literature.